THE 
CHEMISTRY  AND   MANUFACTURE 


OF 


HYDROGEN 


BY 


P.  LITHERLAND  TEED 

,  » 

A.R.S.M.  (MINING  AND  METALLURGY),  A.I.M.M. 
MAJOR,  R.A.F. 


NEW  YORK 

LONGMANS,     GREEN      AND     CO. 
LONDON:    EDWARD   ARNOLD 

1919 


DEDICATED    TO 

BRIG.-GENS.  E.   M.   MAITLAND,  C.M.G.,  D.S.O.,  R.A.F. 

AND 

E.  A.  D.  MASTERMAN,  C.B.E,  A.F.C,  R.A.F. 


415491 


PREFACE. 

THOUGH  our  national  requirements  are  perhaps  the 
greatest,  it  is  noteworthy  that  our  contribution  to  the 
technology  of  hydrogen  is  probably  the  least  of  any 
of  the  Great  Powers  ;  so,  should  it  happen  that  this 
work  in  any  way  stimulates  interest,  resulting  in 
further  improvement  in  the  technology  of  the  subject, 
the  author  will  feel  himself  more  than  amply  rewarded. 
The  author  would  like  to  express  his  thanks  to 
the  Director  of  Airship  Production  for  permission  to 
publish  this  book,  and  to  Major  L.  Rutty,  R.A.F., 
for  many  helpful  suggestions  in  the  compilation  of 
the  text  and  assistance  in  correcting  the  proofs. 

P.   L.  T. 

EYNSFORD,  KENT. 


CONTENTS. 

CHAP.  PAGE 

I.  HYDROGEN — ITS   USES — DISCOVERY,    AND   OCCURRENCE 

IN  NATURE .         .         i 

II.  THE  CHEMICAL  PROPERTIES  OF  HYDROGEN  ...         9 

III.  THE      MANUFACTURE      OF   *  HYDROGEN.        CHEMICAL 

METHODS          .         .         .         .         .         .         .         .       39 

IV.  THE  MANUFACTURE  OF  HYDROGEN.     CHEMICO- PHYSICAL 

METHODS          .         .         .         .         .         .         .         .113 

V.  THE  MANUFACTURE  OF  HYDROGEN.     PHYSICAL  METHODS     126 
APPENDIX.     PHYSICAL  CONSTANTS        ,         ,         .         .145 


vii 


CHAPTER  I. 

HYDROGEN— ITS     USES— DISCOVERY,      AND     OCCUR- 
RENCE IN  NATURE. 

The  Uses  of  Hydrogen, — The  commercial  pro- 
duction of  hydrogen  has  received  a  great  stimulus  dur- 
ing the  last  few  years  owing  to  its  being  required  for 
industrial  and  war  purposes  in  quantities  never  previously 
anticipated. 

The  discoveries  of  M.  Sabatier  with  regard  to  the 
conversion  of  olein  and  other  unsaturated  fats  and  their 
corresponding  acids  into  stearin  or  stearic  acid  have 
created  an  enormous  demand  for  hydrogen  in  every  in- 
dustrial country  ; x  the  synthetic  production  of  ammonia 
by  the  Haber  process  has  produced  another  industry 
with  great  hydrogen  requirements,  while  the  Great  War 
has,  through  the  development  of  the  kite  balloon  and 
airship,  made  requirements  for  hydrogen  in  excess  of 
the  two  previously  mentioned  industries  combined. 

The  increase  in  hydrogen  production  has  modified 
the  older  processes  by  which  it  was  made,  and  has  also 
led  to  the  invention  of  new  processes,  with  the  result 
that  the  cost  of  production  has  decreased  and  will  prob- 
ably continue  to  decrease,  thus  allowing  of  its  employ- 
ment in  yet  new  industries. 

1  The  weight  of  oil  hardened  by  means  of  hydrogen  in  Europe 
in  1914  probably  exceeded  250,000  tons. 

I 


The  Discovery  of  Hydrogen. — The  discovery  of 
hydrogen  should  be  attributed  to  Turquet  de  Mayerne,1 
who  in  1650  obtained,  by  the  action  of  dilute  sulphuric 
acid  on  iron,  a  gas,  or  "  inflammable  air,"  which  we  now 
know  to  have  been  hydrogen. 

Turquet  de  Mayerne  recognised  the  gas  he  obtained 
as  a  distinct  substance.  Robert  Boyle 2  made  some 
experiments  with  it,  but  many  of  its  more  important 
properties  were  not  discovered  until  Cavendish's  investi- 
gations,3 beginning  in  1766  ;  while  the  actual  name 
"  Hydrogen,"  meaning  "  water  former,"  was  given  to 
the  gas  by  Lavoisier,  who  may  be  regarded  as  the  first 
philosopher  to  recognise  its  elemental  nature. 

Occurrence  in  Nature. 

Hydrogen  occurs  in  small  quantities  in  Nature  in 
the  uncombined  state.  It  is  found  in  a  state  of  con- 
densation in  many  rocks  and  in  some  specimens  of 
meteoric  iron.  It  is  present  in  the  gaseous  discharges 
from  oil  and  gas  wells  and  volcanoes,  and  is  also  a  con- 
stituent to  a  very  minute  extent  of  the  atmosphere. 

Hydrogen  in  the  uncombined  state  exists  in  enor- 
mous masses  upon  the  sun,  and  is  present  in  the 
"  prominences "  observed  in  solar  eclipses,  while  by 
optical  means  it  may  also  be  detected  in  many  stars  and 
nebulae. 

1  Paracelsus,  in  a  similar  experiment  in  the  sixteenth  century, 
obtained  the  same  gas,  but  failed  to  recognise  it  as  a  distinct  sub- 
stance. 

2  "  New  Experiments  touching  the  Relation  between  Flame  and 
Air,"  by  the  Hon.  Robert  Boyle,  1672. 

3  James  Watt,  the  discoverer  of  the  steam  engine,  did  many  similar 
experiments  about  the  same  time,  but  his  interpretation  of  his  results 
was  confused  by  his  over-elaborate  theories. 


OCCURRENCE  IN  NATURE 


In  the  combined  state  hydrogen  is  extremely  abun- 
dant. It  is  present  to  the  extent  of  one  part  in  nine  (by 
weight)  in  water,  and  is  a  constituent  of  all  acids  and 
most  organic  compounds. 

In  Rocks. — In  a  state  of  "occlusion,"  or  molecular 
condensation,  hydrogen  is  to  be  found  in  most  igneous 
rocks  in  association  with  other  gases,  the  total  volume 
of  occluded  gases  being  on  the  average  about  4*5  times 
the  volume  of  the  rock. 

The  following  analyses  of  Sir  William  Tilden  *  give 
the  composition  of  the  occluded  gases  in  several  rocks 
from  different  parts  of  the  world  : — 


Rock. 

Where  From. 

Carbon 
Dioxide. 

Carbon 
Monoxide. 

Methane. 

Nitro- 
gen. 

Hydro- 
gen. 

Granite  . 
Gabbro  . 

Skye   .         . 
Lizard 

23-6 

5*5 

6'45 

2-l6 

3-02 
2-03 

5-13 
I'QO 

61-68 
88-42 

Pyroxene 

Ceylon 

772 

8«o6 

•56 

ri6 

1  2  '49 

gneiss  . 

Gneiss    . 

Seringpatam 

31*62 

5-36 

"Si 

•56 

61-93 

Basalt     . 

Antrim 

32-08 

2O'O8 

lO'OO 

1-61 

36-15 

In  Meteoric  Iron, — An  examination  of  certain 
meteoric  irons,  made  by  Sir  William  Ramsay  and  Dr. 
Travers,2  showed  that  these  contained  occluded  gas,  and 
that  this  gas  was  hydrogen  : — 


Description  of 
Meteorite. 

Weight  Taken. 

Hydrogen  Evolved. 

Toluca 
Charca 
Rancho  de  la  Pila 

i  grm. 
M 
» 

2-8  C.C. 
•28,, 

•57  » 

1  "  Proc.  Roy.  Soc.,"  1897. 


4  HYDROGEN 

Observing  that  meteoric  iron  contains  occluded 
hydrogen,  it  is  interesting  to  note  that  the  examination 
of  steel  shows  that  it  also  possesses  this  property  of  con- 
densing gases.  Steel  of  the  following  composition— 

Per  Cent. 
Combined  carbon       .         .         .          .          .         .          *8io 

Silicon       .         .          .         .          .       •  .          .         •          *o8o 

Manganese         .          .          .          .         .          .          .          '050 

Sulphur '028 

Phosphorus -019 

Iron  (by  difference)   .         .         .         .         .         .99*013 


lOO'OOO 


in  pieces  6  x  i  x  i  cm.  was  heated  (ultimate  temperature 
979°  C.)  for  ten  days  in  vacuo  and  the  gases  evolved 
analysed,  with  the  result  that  they  were  found  to  have 
the  following  composition  : — 

Per  Cent, 
by  Volume. 

Hydrogen 52*00 

Carbon  monoxide       .          .         .          .          .         .       45*52 

„        dioxide  ......          1-68 

Methane  ........  '72 

Nitrogen -08 


lOO'OO 


The  total  weight  of  steel  was  69*31  grammes,  while 
the  total  volume  of  gas  evolved  was  19*86  c.c.1 

An  examination  of  a  defective  Admiralty  bronze 
casting  showed  that  there  was  an  appreciable  quantity 
of  occluded  gas  in  it,  containing  7*6  per  cent,  of  hydro- 
gen by  volume.2 

1  "  Gases  Occluded  in  Steel,"  by  T.  Baker,  Iron  and  Steel  Institute, 
"Carnegie  Scholarship  Memoirs,"  vol.  i.,  1909. 

2  "  An  Investigation  on  Unsound  Castings  of  Admiralty  Bronze," 
by  H.  C.  H.  Carpenter  and  C.  F.  Elam,  Inst.  of  Metals,  1918. 


OCCURRENCE  IN  NATURE 


In  Discharge  from  Oil  and  Gas  Wells. — The 
gas  discharged  from  gas  and  oil  wells  contains  small 
quantities  of  hydrogen,  as  will  be  seen  from  the  follow- 
ing analyses  of  natural  gas  discharges  in  Pennsylvania, 
West  Virginia,  Ohio,  Indiana,  and  Kansas. 

AVERAGE  COMPOSITION  BY  VOLUME.1 


Pa.  &  W.  Va. 

Ohio  &  Ind. 

Kansas. 

Hydrogen        .         .        ~.; 

•10 

I-50 

•oo 

Carbon  dioxide 

"OS 

•20 

•30 

Sulphuretted  hydrogen      . 

•oo 

'IS 

•oo 

Oxygen  .... 

trace 

'IS 

•oo 

Carbon  monoxide    . 

•40 

*5° 

I'OO 

Methane 

80-85 

93-60 

93-65 

Other  hydrocarbons 

14*00 

•30 

•25 

Nitrogen 

4'6o 

3'6o 

4-80 

In  Gases  from  Volcanoes.2 — The  nature  of  the 
gases  discharged  from  volcanoes  has  been  most  care- 
fully studied  from  about  the  middle  of  the  last  century, 
with  the  result  that  the  chemical  composition  of  the  gas 
discharged  has  been  determined  at  many  different  vol- 
canoes, and  at  different  times  at  the  same  volcano. 
From  these  investigations  it  would  appear  that  in  the 
more  violent  discharges  there  are  very  considerable 
amounts  of  hydrogen,  while  in  the  more  placid  eruptions 
there  is  little  gas  of  any  description,  except  steam, 
generally  accompanied  by  water  containing  mineral 
salts. 

1  U.S.A.  Geological   Survey,  "Mineral  Resources  of  U.S.A.," 
1909,  2,  297. 

2  For  further  information  on   this  subject   see    F.  W.  Clarke's 
"The  Data  of  Geochemistry,"  U.S.G.S.,  Bull.  616. 


6  HYDROGEN 

Below  are  given  analyses  of  volcanic  gas  from  differ 
ent  parts  of  the  world  by  different  authorities  :— 

From    a  group   of  fumaroles  at    Reykjalidh,    Ice 
land1  :— 

Hydrogen  ........     25*14 

Oxygen       ........        — 

Nitrogen     ........       072 

Carbon  dioxide  .......     50*00 

Sulphur  dioxide  .......        — 

Sulphuretted  hydrogen         .         .         .         .         .24*12 


Prom  afumarole  on  Mont  Pelee,  Martinique^  :  — 

Hydrogen  ........  8*12 

Oxygen       ........  13-67 

Nitrogen    ........  54-94 

Carbon  dioxide   .......  15*38 

Sulphur  dioxide  .......  — 

Carbon  monoxide        ....          .  1-60 

Sulphuretted  hydrogen         ..... 

Methane     ........  5-46 

Argon         ........  -71 

99-88 

From  Kilauea  3  :  — 
Hydrogen  ........     10-2 

Oxygen       ........       — 

Nitrogen     .         .         .         .         .         .         .         .11*8 

Carbon  dioxide   .......     73-9 

,,       monoxide        ......       4-0 

Sulphur  dioxide  .......        — 

99'9 

1  R.  W.  Bunsen,  "  Annales  Chim.  Phys.,"  3rd  ser.,  vol.  38,  1853. 

2  H.  Moissan,  "Comptes  Rend.,"  vol.  135,  1902. 

3  A.  L.  Day  and  E.  S.  Shepherd,  "  Bull.  Geol.  Soc.  America," 
vol.  24,  1913. 


OCCURRENCE  IN  NATURE 

From  Santorin l : — 

Hydrogen 29-43 

Oxygen       .                  .         ...  .  '32 

Nitrogen     .         .                  .         .         .         .  .  32-97 

Carbon  dioxide  .         .         .         .         .         .  .36-42 

Carbon  monoxide       .         .         ,         .  .  — 

Methane     .         .         .         .         .         .         .  .  -86 

Sulphuretted  hydrogen       '...'..-        .  .  — 


lOO'OO 


In  Clays* — Not  only  is  hydrogen  present  in  most 
igneous  rocks,  but  it  is  to  be  found  to  a  small  extent 
in  some  clays.  Sir  William  Crooks,  O.M.,  F.R.S., 
was  kind  enough  to  investigate  for  the  author  the 
gases  occluded  in  the  celebrated  "  Blue  Ground" — 
a  clay  in  which  the  Kimberley  diamonds  are  found. 
This  clay  was  found  to  contain  gas  composed  of  82 
per  cent,  of  carbon  dioxide,  the  bulk  of  the  residue 
being  oxygen  and  nitrogen,  with  detectable  traces  of 
hydrogen. 

In  Air. — As  is  not  surprising,  hydrogen  is  present 
in  the  atmosphere  to  a  very  small  extent,  as  will  be 
seen  from  the  following  analysis  of  air  under  average 
conditions.  It  is  doubtless  derived  from  the  sources 
already  mentioned,  and  also  from  the  decay  of  organic 
matter  containing  hydrogen. 

The  following  represents  the  average  composition  of 
normal  air  : — 

Volumes  per  1000. 

Nitrogen  .  .  ,  ,  ...  769-500 
Oxygen  .  .  .  .  .  ,  .  206-594 
Aqueous  vapour 14-000 

1  F.  Fouque,  "  Santorin  et  ses  eruptions,"  Paris,  1879. 


HYDROGEN 

Volumes  per  1000. 

Argon          .  9.358 

Carbon  dioxide     ......  -336 

Hydrogen    .         .         .         .         .         .         .  -19 

Ammonia    .......  -008 

Ozone          .......  '0015 

Nitric  acid '0005 

Neon  ........  -oi 

Helium        .......  -ooi 

Krypton -ooi 

Xenon         .......  '00005 


CHAPTER  II. 

THE  CHEMICAL  PROPERTIES  OF  HYDROGEN. 

HYDROGEN  in  the  free  state  has  a  capability  of  enter- 
ing into  combination  with  a  large  variety  of  substances, 
forming  chemical  compounds,  while  hydrogen  in  the 
combined  state  reacts  with  many  other  chemical  com- 
pounds, forming  new  compounds. 

Reaction  of  Hydrogen  with  Oxygen  in  the  Free 

State. 

By  far  the  most  important  chemical  reaction  of  hy- 
drogen is  undoubtedly  that  which  it  enters  into  with 
oxygen.  When  hydrogen  is  mixed  with  oxygen  and 
the  temperature  of  the  mixed  gases  raised,  they  com- 
bine with  explosive  violence,  producing  steam.  This 
reaction  may  be  expressed  by  the  following  equation  : — 
2H2  +  O2  =  2H2O. 

If  a  stream  of  hydrogen  issues  into  air  and  a  light  is 
applied  to  it,  it  burns  (in  accordance  with  the  above 
equation)  with  an  almost  non-luminous  flame.  (This 
reaction  is,  of  course,  reversible,  i.e.  a  stream  of  air 
would  burn  in  the  same  way  in  an  atmosphere  of  hy- 
drogen.) It  was  discovered  by  Frankland  l  that  while 
at  atmospheric  pressure  the  flame  of  hydrogen  burning 
in  oxygen  is  almost  non-luminous  if  the  pressure  is 

1  "Proc.  Royal  Soc.,"  vol.  xvi.,  p.  419. 
(9) 


io  HYDROGEN 

increased  to  two  atmospheres  the  fiame  is  strongly 
luminous. 

The  combination  of  oxygen  and  hydrogen  is  most 
violent  if  the  two  gases  are  present  in  the  relative 
quantities  given  in  the  equation,  viz.  two  volumes  of 
hydrogen  and  one  of  oxygen.  If  one  or  other  of  the 
gases  is  in  excess  of  these  quantities  the  violence  of  the 
reaction  is  reduced  and  the  quantity  of  the  gas  in  excess 
of  that  required  by  the  equation  remains  as  a  residue. 
When  one  gas  is  enormously  in  excess  of  the  other 
a  condition  may  arise  in  which  the  dilution  is  so  great 
that  on  sparking  the  mixture  no  reaction  takes  place.1 
Mixtures  of  air  and  hydrogen  in  which  the  air  is  under 
20  per  cent.  (i.e.  under  4  per  cent,  of  oxygen)  of  the 
total  volume  behave  in  this  way. 

This  point  is  of  importance  in  airships,  as,  providing 
the  purity  of  the  hydrogen  in  the  envelope  is  above 
80  per  cent,  by  volume,  an  internal  spark  in  the  envelope 
will  not  cause  an  explosion,  but  if  the  quantity  of 
hydrogen  by  volume  falls  below  this  amount  there  is  a 
risk  of  explosion  ;  hence  the  procedure  of  deflating 
airships  when  the  purity  has  dropped  to  80  per  cent, 
hydrogen  by  volume. 

The  Temperature  of  Ignition  of  Hydrogen  and 

Oxygen* — When  the  two  gases  are  mixed  in  the  pro- 
portion of  two  volumes  of  hydrogen  and  one  volume 
of  oxygen  it  has  been  found  that  the  temperature  of 
the  mixed  gases  must  be  raised  to  about  580°  C.2 

1  Schoop  states  that  when  either  gas  contains  6  to  8  per  cent, 
of  the  other  it  is  explosive. 

2  Victor  Meyer,  "Berichte,"  No.  16,  1893,  gives  the  temperature 
of  violent  reaction  as  612-15°  C.     Gautier  and  Helier,  "Comptes 
Rend,"  125,  271,  1897,  give  about  550°  C. 


CHEMICAL  PROPERTIES  n 

before  explosion  takes  place.  However,  Professor 
Baker  l  has  shown  that,  if  the  two  gases  are  not  only 
perfectly  pure  but  also  perfectly  dry  (dried  by  being 
kept  in  contact  for  as  long  as  three  weeks  with  anhydrous 
phosphoric  acid)  at  the  temperature  of  1000°  C.,  they 
do  not  combine,  but  even  in  this  dry  condition  they 
will  explode  with  an  electric  spark.2  This  phenomenon 
is  of  great  interest,  and  opens  a  wide  field  of  philosophic 
speculation,  but  the  conditions  of  purity  and  dryness  are 
such  that  this  high  temperature  of  ignition  can  never 
be  attained  under  commercial  conditions. 

Professor  Baker  has  also  shown  that,  when  a  mixture 
of  ordinary  hydrogen  and  oxygen  is  exposed  to  the  in- 
fluence of  strong  sunlight,  the  two  gases  very  slowly 
react,  with  the  production  of  water  in  minute  quan- 
tities. 

In  the  experiment  by  .which  Professor  Baker  made 
this  discovery  he  placed  a  mixture  of  these  two  gases  in 
a  state  of  great  purity  but  not  of  absolute  dryness  (in 
the  ratio  of  two  volumes  of  hydrogen  and  one  of 
oxygen)  in  a  hard  glass  tube  closed  at  one  end  and 
sealed  at  the  other  by  mercury.  This  tube  was  exposed 
outside  a  south  window  for  four  months,  from  September 
to  December,  at  the  end  of  which  time  it  was  found, 
after  due  correction  for  temperature  and  pressure,  that 
the  mixture  of  the  two  gases  had  contracted  by  J^  of  its 
original  volume 3  by  the  formation  of  water.  A  similar 
experiment  with  the  gases  in  an  exceptionally  dry  state, 

1<<Jour.  Chem.  Soc.,"  April,  1902. 

2Dixon,  "Jour.  Chem.  Soc.,"  vols.  97  and  98. 

3  The  volume  of  the  resulting  water  is  almost  negligible,  as 
one  volume  of  hydrogen  and  oxygen  in  the  ratio  stated  produces 
only  -006  volume  (approximately)  of  water. 


12 


HYDROGEN 


but  otherwise  under  exactly  similar  conditions,  showed 
no  such  contraction. 

Whether  the  union  of  hydrogen  with  the  infiltrating 
oxygen  of  the  atmosphere  takes  place  in  airship  envel- 
opes, which  are  comparatively  transparent,  has  not  been 
determined,  but  since  in  airship  practice  there  is  never 
more  than  4  per  cent,  of  oxygen  in  the  envelope,  it  is 


oou 
555 
550 

545 
^ 

^540 

|535 
|530 
^525 

:|520 

•!' 
^515 

510 
505 
500 

. 

I 

\ 

\ 

\ 

\ 

^s 

^^ 

\. 

^ 

\ 

^> 

\ 

"'^ 

"^ 

-^ 

-^. 

^-^ 

•*>—  « 

)              50            100           150           200           250           300           350           40 
Volumes  of02  to  100  Volumes  ofH2 

FIG.  i. 

to  be  anticipated  that  such  action,  if  it  took  place,  would 
of  necessity  be  relatively  slower. 

The  temperature  of  ignition  of  varying  mixtures  of 
hydrogen  and  oxygen  has  been  most  carefully  studied 
by  Professor  H.  B.  Dixon,1  who,  besides  much  very  in- 
genious apparatus,  employed  the  cinematograph  for  ob- 
taining conclusive  evidence  of  the  conditions  prevailing 
during  explosion. 


1  " 


Jour.  Chem.  Soc.,"  vols.  97  and  98,  and  vols.  99  and  100. 


CHEMICAL  PROPERTIES 


By  means  of  adiabatic  compression,  the  temperature 
of  ignition  of  different  mixtures  of  hydrogen  and  oxygen 
was  determined,  with  results  which  may  be  seen  in 
Fig.  i.  From  a  study  of  this  curve  it  will  be  noticed 
that  the  most  easily  ignited  mixture  is  not  one  in  which 
the  proportion  of  hydrogen  to  oxygen  is  as  two  to  one, 
as  might  perhaps  be  expected,  but  when  the  ratio  is 
one  volume  of  hydrogen  to  four  of  oxygen. 

IGNITION  TEMPERATURES  OF  HYDROGEN  AND  OXYGEN  MIXTURES. 
(As  determined  by  Prof.  H.  B.  Dixon,  M.A.,  F.R.S.) 

(Ignition  by  Adiabatic  Compression?) 


Composition  of  Mixture. 
By  Volume. 

Ignition 
Temperature. 

Oxygen. 

Hydrogen. 

0  Centigrade. 

33*33 

IOO 

557 

40 

542 

50 

536 

IOO 

530 

150 

525 

2OO 

520 

250 

516 

300 

512 

350 

509 

4OO 

507 

The  temperature  of  ignition  of  a  mixture  fired  by 
adiabatic  compression  is  lower  than  when  the  same 
mixture  is  fired  by  being  heated  in  a  glass  or  silica  tube 
at  atmospheric  pressure.  Professor  H.  B.  Dixon  in  a 
private  communication  to  the  author  states  that  he  found 
the  ignition  temperature  of  electrolytic  gas  under  the 
latter  conditions  to  be  580°  C. 


HYDROGEN 


Besides  studying  the  temperature  of  ignition  of 
various  gaseous  mixtures  Professor  H.  B.  Dixon  in- 
vestigated the  nature  of  explosions1  and  found  that 
Berthelot's  conception  of  an  explosion  as  being  an  ad- 
vancing locus  of  high  pressure  and  of  rapid  chemical 
change,  which  he  described  as  "1'onde  explosive,"  was 
fundamentally  correct. 

Without  going  into  detail  with  regard  to  this  very 
interesting  subject,  it  may  be  stated  that  "  the  velocity  of 
the  explosion  wave  in  a  gaseous  mixture  is  nearly  equal 
to  the  velocity  of  sound  in  the  burning  gases". 

While  this  statement  does  not  satisfy  all  cases  of 
gaseous  explosion,  it  may  be  regarded  as  fundamentally 
correct,  exceptions  to  the  rule  being  capable  of  explana- 
tion on  the  basis  of  undoubted  secondary  reactions. 

On  the  basis  of  this  relationship  between  the  velocity 
of  sound  in  the  burning  gases  and  the  velocity  of  ex- 
plosion, Professor  H.  B.  Dixon  calculated  the  velocity 
of  the  explosion  wave  in  certain  gaseous  mixtures  and 
also  determined  it  experimentally,  with  the  results  given 
below : — 


Velocity  of  Explosion  Wave  in 

Metres  per  sec. 

Gas  Mixture. 

Calculated. 

Found. 

8H2  +  O2 

3554 

3535 

H2  +  3O2 

1740 

1712 

While  it  has  been  said  that  the  temperature  of  igni- 

1 "  The  Rate  of  Explosion  in  Gases,"  by  H.  B,  Dixon,  Bakerian 
Lecture,  Phil.  Trans.  Royal  Society,  1893. 


CHEMICAL  PROPERTIES  15 

tion  of  hydrogen  and  oxygen  in  their  most  readily 
ignited  proportions  must  be  at  some  point  at  least  500° 
C.  in  the  mixture  of  the  gases,  this  statement  requires 
modification  in  that,  though  it  is  perfectly  true  in  the  case 
of  a  mixture  of  the  gases  contained  in  glass  or  non- 
porous  vessels,  in  the  presence  of  certain  substances  of 
a  porous  nature  this  temperature  of  ignition  is  greatly 
reduced.  This  is  particularly  so  in  the  case  of  platinum 
in  a  spongy  condition.  If  a  piece  of  spongy  platinum 
is  introduced  at  ordinary  atmospheric  temperature  into 
an  explosive  mixture  of  hydrogen  and  oxygen,  the 
platinum  is  observed  to  glow  and  an  explosion  almost 
immediately  takes  place.  This  property  is  more  marked 
if  the  platinum  is  in  the  spongy  condition,  but  it  is 
equally  true  if  it  is  in  the  form  of  wire  or  foil. 

There  is  no  complete  explanation  of  this  phenomenon, 
but  it  has  been  observed  that  certain  substances  possess 
the  property  of  absorbing  many  times  their  own  volume 
of  different  gases,  and  that  these  absorbed  gases  possess 
a  greatly  increased  chemical  activity  over  their  normal 
activity  at  the  same  temperature.  Neuman  and  Strientz l 
found  that  one  volume  of  various  metals  in  a  fine  state 
of  division  is  capable  of  absorbing  the  following  amounts 
of  hydrogen  : — 

Palladium  black  .  •         «         .         •  502*35  volumes. 

Platinum  sponge  .         .         .         .  49*3  „ 

Gold .  46-3 

Iron   ...  .  19-17  „ 

Nickel  .  17-57  „ 

Copper        .  4-5 

Aluminium          .  :   .         .         .         .  2-72  „ 

Lead.  .        .        f        .  -15  „ 

1  "Zeitschrift  fur  analytische  chemie,"  vol.  32. 


16  HYDROGEN 

This  property  of  certain  substances,  without  them- 
selves undergoing  chemical  change,1  of  being  able  to 
impart  increased  chemical  activity  to  the  gases  they 
absorb  is  not  confined  to  the  metals,  but  is  possessed  by 
charcoal  (particularly  animal  charcoal),  magnesite  brick, 
and  probably  to  some  extent  by  all  porous  substances. 
It  is  a  subject  of  very  great  interest,  and  in  many  cases 
of  practical  importance 2  which  is  now  becoming  a  sub- 
division of  Physical  Chemistry,  under  the  name  of  "  Sur- 
face Energy  ". 

The  Temperature  Produced  by  the  Ignition  of 
Hydrogen  and  Oxygen* — In  the  previous  paragraph 
the  temperature  at  which  the  ignition  of  hydrogen  and 
oxygen  begins  has  been  given,  and  now  the  temperature 
which  the  flame  reaches  will  be  considered. 

Bunsen  determined  the  temperature  of  the  flame 
produced  to  be  : — 

Flame  of  hydrogen  burning  in  air     .         .          .     2024°  C. 

oxygen       .         .     2844°  C. 

A  later  determination  by  Fery  ("  Comptes  Rend.," 
1902,  134,  1201)  gives  the  values  1900°  C.  and  2420°  C. 
respectively,  while  Bauer  (ibid.,  1909,  148,  1756)  ob- 
tained figures  for  hydrogen  burning  in  oxygen  varying 
from  2200°  C.  to  2300°  C.,  according  to  the  proportion  of 
oxygen  present. 

The  reason  that  the  flame  of  hydrogen  burning  in 
oxygen  is  hotter  than  the  flame  produced  in  air  is  due 

1  It  is  contended  by  Troost  and  Hautefeuille  that  in  the  case  of 
palladium  the  absorption  of  the  hydrogen  is  chemical  and  not 
physical,  palladium  hydride  (Pd2H)  being  formed. 

2  The  Bonecourt  flameless  boiler  depends  on  the  surface  energy 
of  magnesite  brick. 


CHEMICAL  PROPERTIES  17 

to  the  fact  that  the  speed  of  burning  in  oxygen  is  greater 
than  in  air,  because  of  the  absence  of  any  dilution,  and 
also  because  the  nitrogen  and  other  inert  constituents 
in  the  air  are  themselves  heated  at  the  expense  of  the 
flame  temperature.1 

The  calculated  value  for  the  flame  temperature  of 
hydrogen  burning  in  air,  assuming  that  the  heat  of 
reaction  is  distributed  among  the  inert  constituents  of 
the  air,  is  1970°  C.  (Le  Chatelier),  and  this  agrees  ap- 
proximately with  the  above  figures  of  2024°  C.  and 
i900°C. 

A  comparison  between  the  flame  temperature  of 
hydrogen  and  other  gases  burning  in  air  is  given  in  the 
following  table  : — 

Hydrogen2           .         ,         .         .  i9oo°C. 

Acetylene3           2548^. 

Alcohol2     .         .         .         .         .         .  i7os°C. 

Carbon  Monoxide  4      .         ,         .         .  2ioo°C. 

The  Quantity  of  Heat  Produced  by  Burning 
Hydrogen. — The  temperature  of  ignition  and  the  flame 
temperature  of  hydrogen  have  already  been  considered. 
It  now  only  remains  for  the  quantity  of  heat  produced 
by  a  given  weight  of  hydrogen  to  be  considered  in 
comparison  with  some  other  gases  combustible  in  air. 

1  In  the  case  of  Zeppelin  airships  brought  down  in  flames,  it  is 
not  surprising  that  considerable  amounts  of  molten  metal  have  been 
found  in  the  locality,  observing  that  the  melting  point  of  aluminium 
is  657°  C.,  copper  1087°  C. 

2  Fery,  I.e. 

3  Fery,  I.e.      The  temperature  of  acetylene  burning  in  oxygen  is 
about  4000°  C.,  but  this  arises  from  circumstances  not  present  in  the 
case  of  hydrogen  flames. 

4  Le  Chatelier. 

2 


1 8  HYDROGEN 

i  Ib.  of  hydrogen  on  combustion  gives  62,100  B.T.U.1 

„        marsh  gas  „  ,,  ,,  24,020        „ 

„        benzene      „  „  „  18,090       „ 

„        carbon  monoxide   „  „  4>38°        » 

Reactions  of  Hydrogen  with  Oxygen  in  the  Com- 
bined State. 

So  far  the  reaction  of  hydrogen  and  oxygen  has 
only  been  considered  when  both  are  in  the  gaseous 
form.  However,  such  is  the  attraction  of  hydrogen 
for  oxygen  that  when  the  latter  is  in  combination 
with  some  other  element  the  hydrogen  will  gener- 
ally combine  with  the  oxygen,  forming  water  and 
leaving  the  substance  formerly  in  combination  with  the 
oxygen  in  a  partially  or  wholly  reduced  state.  Thus, 
oxides  of  such  metals  as  iron,  nickel,  cobalt,  tin,  and  lead 
are  reduced  to  the  metallic  state  by  heating  in  an  at- 
mosphere of  hydrogen. 

Thus  :- 

(1)  Fe203  +  3H2  =  2Fe  +  3H2O 

(2)  NiO  +  H2  =  Ni  +  H2O 

(3)  CoO  +  H2  =  Co  +  H2O 

(4)  SnO2  +  2H2  =  Sn  +  2H2O 

(5)  PbO  +  H2  =  Pb  +  H2O 

The  temperature  at  which  the  reduction  by  the 
hydrogen  takes  place  varies  with  the  different  oxides 
and  also  with  the  same  oxide,  depending  on  its  physical 
condition.  "  Crystalline  haematite,"  as  the  natural  ferric 
oxide  is  called,  requires  to  be  at  a  red  heat  (about  500° 
C.)  before  reduction  begins  to  take  place,  while  if  iron 
is  precipitated  from  one  of  its  salts  (as  ferric  hydrate  by 

1  The  latent  heat  of  the  steam  produced  is  included  in  the  heat 
units  of  fuels  containing  hydrogen. 


CHEMICAL  PROPERTIES  19 

ammonia)  the  resulting  ferric  hydrate  can  be  reduced 
to  the  metallic  state  at  the  temperature  of  boiling  water. 

With  nickel  the  same  variation  of  the  temperature 
of  reduction  is  noted,  depending  on  the  physical  condi- 
tion. Thus  Moisson  states  that  the  sub-oxide  of  nickel 
(NiO)  which  has  not  been  calcined,  is  reduced  by  hydro- 
gen at  230°-240°  C.  ;  Muller,  on  the  other  hand,  states 
that  the  reduction  of  the  oxide  at  this  temperature  is  not 
complete  but  only  partial,  but  that  if  the  temperature  is 
raised  to  270°  C.  a  complete  reduction  takes  place.  If 
the  oxide  of  nickel  has  been  strongly  heated  its  tempera- 
ture of  reduction  to  the  metallic  state  is  at  least  420°  C., 
in  which  case  it  is  quite  unsuitable  for  use  as  the  cata- 
lytic agent  in  the  hydrogenation  of  organic  oils. 

Such  is  the  affinity  of  hydrogen  for  oxygen  that 
hydrogen  will  under  certain  circumstances  reduce  hydro- 
gen peroxide.  If  an  acid  solution  of  hydrogen  peroxide 
is  electrolysed,  oxygen  will  be  liberated  at  the  positive 
pole  (or  anode),  but  no  gas  will  be  liberated  at  the 
negative  (or  cathode),  for  the  hydrogen  which  is  set 
free  there  immediately  reduces  the  hydrogen  peroxide 
in  the  solution  to  water,  as  shown  in  the  following 
equation : — 

H202  +  H2  =  2H20. 

It  has  been  mentioned  that  the  temperature  of  re- 
duction of  the  metallic  oxides  by  hydrogen  varies  with 
the  different  oxides  and  with  the  physical  condition  of 
the  same  oxide.  It  might  further  be  added  that  the 
physical  condition  of  the  hydrogen  also  modifies  the 
temperature  of  reduction.  This  can  be  well  shown  by 
taking  some  artificial  binoxide  of  tin  (SnO2)  and  placing 
it  in  a  metal  tray  in  a  solution  of  slightly  acidulated 
water.  The  metal  tray  is  then  connected  to  the 


2o  HYDROGEN 

negative  pole  of  an  electric  supply,  and  another  con- 
ductor placed  in  the  liquid  connected  to  the  positive  of 
the  supply.  On  the  current  being  switched  on  electrolysis 
takes  place,  that  is  to  say,  the  water  is  decomposed  into 
hydrogen  and  oxygen,  the  hydrogen  being  liberated  on 
the  surface  of  the  metal  tray  containing  the  binoxide  of 
tin,  and  the  oxygen  at  the  other  pole.  The  nascent 
hydrogen  liberated  in  the  neighbourhood  of  the  white 
tin  oxide  reduces  it  on  the  surface  of  the  particle  to 
metallic  tin,  in  accordance  with  the  following  equation  : — 

SnO2  +  2H2  =  Sn  +  2H2O, 

a  fact  which  can  easily  be  proved  by  chemical  means, 
but  which  is  also  detectable  by  the  change  of  the  oxide 
from  white  to  the  dark  grey  of  metallic  tin. 

Chemical  Combination  of  Hydrogen  with  Carbon. 

It  has  been  shown  that  if  hydrogen  is  passed  over 
pure  carbon  heated  to  1150°  C.,  direct  chemical  union 
takes  place,1  methane  or  marsh  gas  being  formed  :— 

C  +  2H2  =  CH4. 

This  reaction  is  of  some  importance,  as  formerly  in  the 
production  of  blue  water  gas  the  presence  of  methane 
was  entirely  accounted  for  by  the  presence  of  hydro- 
carbons in  the  fuel.  However,  the  experiments  of  Bone 
and  Jerdan  show  that  even  if  no  hydrogen  whatever 
were  present  in  the  fuel,  methane  would  be  formed  if 
the  temperature  of  the  fuel  be  sufficient. 

If  the  temperature  of  the  carbon  is  somewhat  hotter 
than  1150°  C,  direct  union  continues  to  take  place,  but 
the  product  of  the  reaction  is  not  methane  but  acetylene. 

and  Jerdan,  "Chem.  Soc.  Trans.,"  71,  41,  1897. 


CHEMICAL  PROPERTIES  21 

Thus  if  a  small  pure  carbon  electric  arc  is  made  in  an 
atmosphere  of  hydrogen,  small  quantities  of  acetylene 
are  produced,  but  no  methane. 

Chemical  Combination  of  Hydrogen  with  Chlorine, 
Bromine,  and  Iodine. 

With  Chlorine. —  Hydrogen  will  combine  with 
chlorine,  in  accordance  with  the  following  chemical 
equation,  to  make  hydrochloric  acid  : — 

H2  +  C12  =  2HC1. 

If  the  two  gases  are  mixed  in  equal  proportions  in  a 
diffused  light  and  are  subjected  to  an  electric  spark,  the 
above  reaction  takes  place  with  explosive  violence.  If 
a  glass  tube  containing  a  mixture  of  the  gases  is  heated, 
the  same  reaction  takes  place  with  violence. 

If  a  mixture  of  hydrogen  and  chlorine  at  atmospheric 
temperature  is  exposed  to  strong  sunlight,  hydrochloric 
acid  is  immediately  formed,  with  the  characteristic  ex- 
plosion. Investigation  of  this  increase  in  the  chemical 
activity  of  hydrogen  and  chlorine  in  the  presence  of 
sunlight  has  shown  that  it  is  the  actinic  rays  which  pro- 
duce the  phenomenon  ;  thus  if  the  rays  which  are  present 
at  the  blue  and  violet  end  of  the  spectrum  are  prevented 
from  reaching  the  mixture  of  the  gases  by  protecting 
this  by  a  red  glass  screen,  no  reaction  between  them 
takes  place.  When  sunlight  is  not  available,  the  ex- 
plosive combination  of  these  two  gases  can  be  shown 
by  exposing  a  mixture  of  them  in  a  glass  vessel  to  the 
light  of  burning  magnesium,  such  as  is  frequently  used 
by  photographers. 

The  remarks  which  have  already  been  made  with 
regard  to  the  reduction  in  chemical  activity  of  hydrogen 


22  HYDROGEN 

and  oxygen  when  perfectly  dry  apply  also  in  the  case 
of  hydrogen  and  chlorine. 

While  referring  to  the  production  of  chemical  union 
between  hydrogen  and  chlorine  brought  about  by  the 
influence  of  light,  attention  may  be  drawn  to  what  is 
known  as  the  "  Draper  Effect,"  which  is  best  demon- 
strated in  the  following  apparatus  : — 


FIG.  2. 
Insolation  Vessel 

The  mixed  gases,  in  the  ratio  of  one  volume  of 
hydrogen  to  one  of  chlorine,  are  contained  in  a  flat  glass 
bulb  A,  called  the  insolation  vessel.  The  lower  part  of 
the  insolation  vessel  usually  contains  some  water  satu- 
rated with  the  two  gases.  The  capillary  tube  BC  con- 
tains a  thread  of  liquid  ac,  to  serve  as  an  index.  Under 
the  influence  of  a  flash  of  light  the  thread  of  liquid  ac  is 
pushed  outwards,  to  return  immediately  to  its  original 
position.  Thus,  a  travels  to  b,  and  immediately  returns 
to  a.  With  every  flash  of  light  the  same  phenomenon 
takes  place.  At  the  time  of  its  discovery  (1843,  "  Phil. 
Mag.,"  1843,  iii-i  23>  4O3>  415)  the  reason  for  this 
sudden  rise  in  pressure  was  not  understood,  but  careful 
investigation  by  J.  W.  Mellor  and  W.  R.  Anderson1 
has  shown  that  at  each  flash  minute  quantities  of  hydro- 
chloric acid  are  formed,  with  the  production  of  a  little 
heat,  thus  causing  a  rise  in  pressure  until  it  is  dispersed 

1  "  Jour.  Chem.  Soc.,"  April,  1902. 


CHEMICAL  PROPERTIES  23 

— in  fact,  the  Draper  effect  may  be  likened  to  a  very 
small  explosion  without  sufficient  energy  to  propagate 
itself  throughout  the  gas. 

Such  is  the  attraction  of  chlorine  for  hydrogen  that 
even  when  the  latter  is  in  combination  with  some  other 
element  the  chlorine  often  will  combine  with  the  hydro- 
gen, liberating  that  element.  Thus,  if  chlorine  is  passed 
through  turpentine,  the  carbon  is  liberated,  in  accordance 
with  the  following  equation  :— 

C10H16  +  80,  =  loC  +  i6HCl. 

Again,  at  ordinary  temperatures  and  in  ordinary  diffused 
light,  but  more  rapidly  in  sunlight  or  other  light  of 
actinic  value,  chlorine  will  decompose  water,  liberating 
oxygen,  in  accordance  with  the  following  equation  :— 

2H2O  +  2C12  =  4HC1  +  O2. 

The  combination  of  hydrogen  with  chlorine  is  at- 
tended with  the  evolution  of  heat.  According  to  Thorn- 
sen,  the  combination  of  i  gramme  of  hydrogen  with 
35*5  grammes  of  chlorine  is  attended  with  the  evolution 
of  22,000  gramme-calories  of  heat. 

With  Bromine, — The  element  bromine  will  combine 
with  hydrogen  to  form  hydrobromic  acid,  in  accordance 
with  the  following  equation  : — 

H2  +  Br2  =  2HBr. 

This  reaction  between  hydrogen  and  bromine  is  in  many 
respects  comparable  with  the  combination  of  hydrogen 
with  chlorine,  but  unlike  the  latter,  the  reaction  cannot 
be  brought  about  by  sunlight.  However,  if  the  two 
gases  are  heated,  they  will  combine,  but  their  combina- 
tion is  attended  with  the  evolution  of  less  heat  than 


24  HYDROGEN 

in  the  case  of  chlorine.  Thomsen  states  that  the  com- 
bination of  i  gramme  of  hydrogen  with  80  grammes 
of  bromine  (liquid)  is  attended  with  the  evolution  of 
8440  gramme-calories  of  heat. 

With  Iodine. — Hydrogen  will  combine  with  iodine, 
in  accordance  with  the  following  equation,  providing 
the  iodine  is  in  the  form  of  vapour  and  the  mixture  of 
the  two  gases  is  strongly  heated  in  the  presence  of 
spongy  platinum  :— 

H2  +  I2  =  2HI. 

Thomsen  has  shown  that  this  combination,  unlike 
the  two  previous  ones,  is  not  attended  with  evolution  of 
heat,  but  by  the  absorption  of  it.  Thus  when  i  gramme 
of  hydrogen  combines  with  127  grammes  of  iodine  (solid), 
6040  gramme-calories  of  heat  are  absorbed. 

Chemical  Combination  of  Hydrogen  with  Sulphur, 
Selenium,  and  Tellurium. 

With  Sulphur. — If  a  mixture  of  sulphur  vapour  and 
hydrogen  is  passed  through  a  tube  heated  to  at  least 
250°  C.,  a  chemical  union  of  the  two  elements  takes 
place,  in  accordance  with  the  equation — 

H2  +  S  =  H2S. 

The  resulting  gas,  which  is  known  as  "  sulphuretted 
hydrogen,"  has  a  characteristic  and  extremely  unpleasant 
odour,  and  is  poisonous  when  inhaled.  According  to 
Th^nard,  respiration  in  an  atmosphere  containing  ^ 
part  of  its  volume  of  sulphuretted  hydrogen  is  fatal  to 
a  dog,  and  smaller  animals  die  when  half  that  quantity 
is  present. 


CHEMICAL  PROPERTIES  25 

Sulphuretted  hydrogen  is  an  inflammable  gas,  and 
will  burn  in  air,  in  accordance  with  the  following  equa- 
tion : — 

2H2S  +  3O2  =  2SO2  +  2H2O, 

producing  sulphur  dioxide  and  water. 

If  the  gas  is  mixed  with  oxygen  in  the  proportions 
required  by  the  equation,  and  subjected  to  an  electric 
spark,  it  explodes  with  violence,  giving  the  same  pro- 
ducts as  when  burnt  in  air. 

Sulphuretted  hydrogen  is  soluble  in  water  at  o°  C. 
to  the  extent  of  4*3706  parts  by  volume  per  unit  volume 
of  water. 

The  density  of  sulphuretted  hydrogen  is  17  times 
that  of  hydrogen. 

With  Selenium. — When  selenium  is  heated  to  250° 
C.  with  hydrogen,  chemical  union  results,  with  the  pro- 
duction of  selenuretted  hydrogen  :— 

H2  +  Se  =  H2Se. 

The  resulting  gas  is  colourless,  resembling  sul- 
phuretted hydrogen  in  smell  and  in  its  chemical  proper- 
ties. It  is,  however,  much  more  poisonous  than  the 
former  gas. 

Selenuretted  hydrogen  is  inflammable  and  burns  in 
the  same  way  as  sulphuretted  hydrogen.  If  the  gas  is 
strongly  heated  it  breaks  up  into  its  two  constituents, 
the  selenium  being  deposited  in  the  crystalline  form. 

Selenuretted  hydrogen  is  soluble  in  water  at  13*2°  C. 
to  the  extent  of  3  "3 1  parts  by  volume  per  unit  volume  of 
water. 

The  density  of  selenuretted  hydrogen  is  40*5  times 
that  of  hydrogen. 


26  HYDROGEN 

With  Tellurium* — When  tellurium  is  heated  to  400° 
C.  in  hydrogen,  the  elements  combine,  forming  hydrogen 
telluride  : — 

H2  +  Te  -  H2Te. 

This  gas,  like  sulphuretted  and  selenuretted  hydrogen, 
is  both  offensive  smelling  and  poisonous.  Like  selenu- 
retted hydrogen,  on  strongly  heating  it  is  decomposed 
into  its  components,  the  tellurium  being  deposited  in 
the  crystalline  form. 

Telluretted  hydrogen  is  soluble  in  water  to  some 
extent,  but  in  course  of  time  the  telluretted  hydrogen  is 
decomposed  and  tellurium  deposited. 

The  density  of  telluretted  hydrogen  is  63*5  times 
that  of  hydrogen. 

Chemical  Combination  of  Hydrogen  with  Nitrogen, 
Phosphorus,  and  Arsenic* 

With  Nitrogen* — Donkin  has  shown  that  when  a 
mixture  of  hydrogen  and  nitrogen  is  subjected  to  the 
silent  electric  discharge,  a  partial  union  of  the  two  gases 
takes  place,  with  the  formation  of  ammonia  : — 
N2  +  3H2  =  2NH3. 

However,  this  reaction  could  in  no  way  be  regarded  as 
commercial,  as  the  quantity  of  ammonia  produced  after 
the  gases  have  long  been  subjected  to  the  silent  electric 
discharge  is  only  just  sufficient  to  be  identified  by  the 
most  delicate  means. 

Recent  investigations  have,  however,  shown  that  if 
the  two  gases  are  mixed  and  subjected  to  very  great 
pressure  (1800  Ib.  per  sq.  inch)  in  the  presence  of  a 
catalytic  agent,  union  to  an  appreciable  extent  takes 
place.  This  process,  which  is  now  being  used  on  a 


CHEMICAL  PROPERTIES  27 

commercial  scale  in  Germany,  is  known  as  the  Haber 
process,  but  few  details  as  to  the  method  of  operation 
are  available.  In  the  earlier  stages  of  the  working  of 
this  process  the  catalytic  agent  was  probably  osmium, 
but  it  is  considered  doubtful  if  this  is  still  being  em- 
ployed. 

THE  USES  OF  AMMONIA. 

Such  is  the  importance  of  ammonia  in  the  existence 
of  a  modern  country  that  it  is  desirable  that  some  ac- 
count of  its  use  should  be  given,  observing  that  it  is  not 
improbable  that  the  Haber  process  may  be  put  into 
operation  in  this  country  in  the  near  future,  consequently 
enormously  increasing  the  demand  for  the  commercial 
production  of  hydrogen. 

Ammonia  or  its  salts  are  employed  in  a  variety  of 
ways  in  many  trades.  From  it  nitric  acid,  the  vital 
necessity  for  the  manufacture  of  all-high  explosives,  can 
be  made ;  it  is  an  essential  for  the  Brunner  Mond  or 
Solvay  ammonia  soda  process  for  the  production  of 
alkali ;  in  the  liquid  form  it  is  employed  all  over  the 
world  in  refrigerating  machinery,  but  its  enormous  and 
increasing  use  is  in  agriculture,  where,  in  the  form  of  sul- 
phate of  ammonia,  it  constitutes  one  of,  if  not  the  most 
important  chemical  manures  known  to  man.  During 
the  year  1916  350,000  tons  of  ammonium  sulphate 
were  produced  in  this  country,  the  larger  proportion  of 
which  was  consumed  in  agriculture — a  proportion  likely 
to  increase  and  not  diminish  if  the  demand  for  home 
production  of  food  continues. 

PROPERTIES  OF  AMMONIA. 

Ammonia  is  a  strongly  smelling  gas,  possessing  a 
most  characteristic  odour.  It  is  lighter  than  air  ;  taking 


28 


HYDROGEN 


the  density  of  hydrogen  as  i,  air  is  14*39,  and  ammonia 
8*5.  Ammonia  is  not  in  the  ordinary  sense  combustible 
in  air,  but  if  the  air  is  heated  or  oxygen  is  supplied  it 
will  burn  with  a  feeble,  almost  non-luminous  flame,  in 
accordance  with  the  following  equation  : — 

4NH3  +  3O2  =  2N2  +  6H20. 

Ammonia  is  strongly  basic,  i.e.  it  possesses  the 
property  of  combining  with  acids  to  make  neutral  salts. 
Thus  with  the  common  acids — sulphuric  acid,  hydro- 
chloric acid  and  nitric  acid — it  forms  salts,  in  accordance 
with  the  following  equations  : — 

2NH3  +  H2S04  =  (NH4)2SO4, 
NH3  +  HC1  =  (NH4)C1, 
NH3  +  HN03  =  (NH4)N03. 

Among  the  physical  properties  of  ammonia  the  out- 
standing features  are  its  solubility  in  water,  its  absorp- 
tion by  charcoal,  and  its  liquefaction. 

Solubility  of  Ammonia  in  Water.  —  Ammonia  is 
very  soluble  in  water.  Its  solubility  decreases  with 
increase  of  temperature,  and,  as  is  of  course  natural, 
increases  with  increase  of  pressure.  The  following 
table  for  the  solubility  of  ammonia  in  water  is 
interesting  :— 


Temperature. 

Grammes  of  NH3 
Dissolved  in  i  c.c. 
of  Water. 

C.c.  of  NH3  at. 
o°  C.  and  760  mm. 

o°C. 

•375 

1148 

8 

713 

923 

16 

•582 

764 

30 

•403 

529 

50 

•229 

306 

CHEMICAL  PROPERTIES  29 

A  feature  of  the  absorption  of  ammonia  by  water  is 
the  reduction  of  the  specific  gravity  of  the  solution. 
Thus  at  15°  C.  a  saturated  solution  containing  34*95  per 
cent,  of  the  gas  by  weight  has  a  density  of  "882,  while 
pure  water  at  the  same  temperature  has  a  density  of 
•99909. 

Absorption  of  Ammonia  by  Charcoal. — Reference  to 
the  surface  energy  of  charcoal  has  already  been  made. 
Its  absorption  of  ammonia  is  very  considerable,  but  varies 
with  the  physical  condition  of  the  charcoal,  as  well  as 
with  the  material  from  which  it  has  been  made.  Saussure 
found  that  freshly  ignited  boxwood  absorbs  about  90 
times  its  own  volume  of  ammonia,  while  Hunter  has 
shown  that  freshly  prepared  charcoal  made  from  cocoa- 
nut  shell  absorbs  about  171  times  its  own  volume  of 
ammonia. 

Liquefaction  of  Ammonia. — Ammonia  is  an  easily 
liquefiable  gas,  and  consequently  it  is  owing  to  this 
property  that  it  is  employed  in  refrigerating  plants  on 
land  and  in  ships,  for  by  the  rapid  evaporation  of  the 
liquid  gas  a  high  degree  of  cold  may  be  obtained.  The 
critical  temperature  of  ammonia,  i.e.  that  temperature 
above  which  by  mere  pressure  it  cannot  be  liquefied,  is 
1 3 1  °  C.  At  this  temperature  a  pressure  of  approximately 
1700  Ib.  per  sq.  inch  must  be  applied  to  produce  lique- 
faction ;  if,  however,  the  temperature  is  below  the 
critical  one  for  the  gas,  the  pressure  required  for  lique- 
faction is  greatly  reduced.  Thus,  if  the  ammonia  is 
cooled  to  15*5°  C.,  a  pressure  of  101  Ib.  per  sq.  inch  is 
required,  while  if  the  gas  is  cooled  to  o°  C.,  a  pressure 
of  only  6 1  *8  Ib.  per  sq.  inch  will  effect  liquefaction. 
Liquid  ammonia  is  a  colourless,  mobile  liquid.  It  boils 
at  "  337°  C.,  and  at  o°C.  has  a  specific  gravity  of  0*62 34. 


30  HYDROGEN 

At  -  75°  C.  liquid  ammonia  solidifies  into  a  white  crystal- 
line solid. 

With  Phosphorus* — If  red  phosphorus   is   gently 

heated  in  a  stream  of  hydrogen,  direct  chemical  union 

takes  place  to  a  small  extent,  with  the  production  of  a  gas 

termed  "  Phosphoretted  Hydrogen  "  or  "  Phosphine  "  :— 

2P  +  3H2  =  2PH3. 

Phosphine  is  an  offensive  smelling,  poisonous  gas 
which  in  the  pure  state  is  not  spontaneously  inflammable. 
However,  its  temperature  of  ignition  is  very  low  ;  thus, 
if  a  stream  of  phosphine  is  allowed  to  impinge  in  air  on 
a  glass  vessel  containing  boiling  water,  it  will  immediately 
burst  into  flame,  burning  with  considerable  luminosity, 
in  accordance  with  the  equation  : — 

PH3  +  2O2  =  HPO3  +  H2O. 

Phosphine  possesses  an  exceedingly  interesting  re- 
action with  oxygen.  Thus,  if  a  mixture  of  phosphine 
and  oxygen  is  subjected  to  a  sudden  reduction  in  pressure 
at  ordinary  atmospheric  temperature,  chemical  combina- 
tion immediately  takes  place  with  explosive  violence,  in 
accordance  with  the  equation  already  given. 

Phosphine,  which  is  produced  in  small  quantities  in 
the  Silicol  process  for  making  hydrogen,1  has  under 
certain  conditions  a  deteriorating  effect  on  cotton  fabrics, 
not  as  an  immediate  action  but  as  a  secondary  reaction. 
The  examination  of  a  balloon  envelope  which  burst  at 
Milan  2  in  1906  showed  that  at  some  spots  the  material 
could  be  easily  torn,  while  over  the  greater  portion  it 

1  The  total  volume  of  phosphine  and  arsine  does  not  exceed 
•025  per  cent,  and  is  usually  about  -01  per  cent. 

2Namias,  "L'Ind.  Chim.,"  1907,  7,  257-258;  "  Chem.   Cent.," 

1907,   2,   1460-1461. 


CHEMICAL  PROPERTIES  31 

showed  a  great  resistance  to  tearing.  The  damaged 
spots  were  found  to  be  impregnated  with  phosphoric 
acid  and  arsenic  acid,  produced  by  the  oxidation  of  the 
phosphine  and  arsine  contained  in  the  hydrogen  with 
which  the  balloon  had  been  inflated. 

Phosphine  in  small  quantities  in  hydrogen  contain- 
ing over  i  per  cent,  of  oxygen  attacks  copper,  producing 
an  acid  liquid  which  has  a  most  corrosive  action  on 
fabric.  However,  it  does  not  appear  under  these  cir- 
cumstances to  have  any  action  on  aluminium  or  zinc  ; 
consequently  any  metal  parts  inside  the  envelope  of 
an  airship  should  be  of  aluminium.  Phosphine  under 
the  above  conditions  attacks  hemp  and  other  textiles 
which  have  been  treated  with  copper  compounds, 
but  it  does  not  appear  to  have  any  action  on  fabrics 
free  from  copper  compounds  or  copper  or  brass 
fastenings. 

Though  it  has  been  stated  that  phosphine  is  not 
spontaneously  inflammable,  with  quite  small  admixtures 
of  liquid  hydrogen  phosphide  it  immediately  bursts  into 
flame  on  coming  into  contact  with  air. 

Phosphine  produced  by  the  reaction  of  water  on 
calcium  phosphide  always  contains  a  quantity  of  the 
liquid  hydrogen  phosphide  sufficient  to  make  the  gas 
spontaneously  inflammable.  Use  of  this  property  is 
made  in  the  Holmes'  Light  used  at  sea  as  a  distress 
signal,  and  also  as  a  marker  at  torpedo  practice. 

Phosphine  is  soluble  in  water  to  a  slight  extent. 
The  solution  of  phosphine  in  water  is  not  very  stable, 
particularly  in  strong  light,  when  it  breaks  up,  deposit- 
ing red  phosphorus. 

The  density  of  phosphine  is  17*5  times  that  of 
hydrogen. 


32  HYDROGEN 

With  Arsenic. — Hydrogen  does  not  directly  com- 
bine with  arsenic,  but  if  an  arsenic  compound  is  in  solu- 
tion in  a  liquid  in  which  hydrogen  is  being  generated, 
i.e.  hydrogen  in  the  nascent  state,  chemical  union  takes 
place.  Thus,  if  arsenious  oxide  is  dissolved  in  dilute 
hydrochloric  acid  and  a  piece  of  metallic  zinc  is  added, 
the  hydrogen  produced  by  the  action  of  the  acid  on  the 
zinc  will  combine  with  the  arsenic,  in  accordance  with 
the  following  equation  :— 

As4O6  +  i2H2  =  4AsH3  +  6H2O. 

The  gas  produced,  which  is  called  "  Arsine "  or 
"  Arsenuretted  Hydrogen,"  is  unpleasant  smelling  and 
poisonous.  It  burns  in  air  with  a  lilac-coloured  but  not 
very  luminous  flame,  thus  : — 

4AsH3  +  6O2  =  As4O6  +  6H2O. 

If  the  gas  is  strongly  heated  it   is   decomposed    and 
elemental  arsenic  deposited. 

Arsine  is  produced  to  a  small  extent  in  the  Silicol 
process  of  making  hydrogen,  and  has  a  deteriorating 
effect  on  fabric  (see  phosphine),  while  with  many  metals 
it  is  decomposed,  arsenic  being  deposited  and  hydrogen 
liberated.  It  can  be  liquefied  easily  (the  liquid  gas 
boiling  at  -  54*8°  C),  and  it  solidifies  at  -  113*5°  C. 
Arsine  is  soluble  in  water,  one  volume  of  water  at  o°  C. 
dissolving  5  volumes  of  arsine.  The  density  of  arsine 
is  39  times  that  of  hydrogen. 

Chemical  Combination  of  Hydrogen  with  Lithium, 
Sodium,  Potassium,  Magnesium,  Calcium,  and 
Cerium, 

The  chemical  combination  of  hydrogen  has  so  far 
only  been  considered  with  regard  to  a  few  non-metallic 


CHEMICAL  PROPERTIES  33 

elements,  but  now  a  new  series  of  reactions  will  be  con- 
sidered in  which  hydrogen  combines  chemically  with  a 
metal.  These  metals  are  those  of  the  alkaline  and 
alkaline  earth  group. 

With  Lithium. — If  hydrogen  is  passed  over  metallic 
lithium  at  about  200°  C.,  the  hydrogen  is  absorbed,  not 
as  hydrogen  is  absorbed  by  platinum,  etc.,  but  chemi- 
cally absorbed,  in  accordance  with  the  following  equa- 
tion : — 

4-Li  +  H2  =  Li4H2. 

If  the  resulting  lithium  hydride  is  allowed  to  cool  and 
is  placed  in  water  it  becomes  a  source  of  hydrogen,  not 
only  giving  up  what  it  has  already  received,  but  also  a 
volume  twice  as  much  as  this,  which  it  has  derived  from 
the  water,  as  may  be  seen  in  the  following  equation  :— 

Li4H2  +  4H2O  =  4L1OH  +  3H2. 

With  Sodium. — Under  similar  circumstances  the 
metal  sodium  absorbs  hydrogen  with  the  production  of 
a  hydride  : — 

4Na  +  H2  =  Na4H2. 

This  hydride,  like  that  of  lithium,  behaves  in  a  similar 
manner  with  water.  It,  however,  has  another  interesting 
property  in  that  if  sodium  hydride  is  heated  in  vacuo  to 
about  300°  C.,  the  whole  of  the  hydrogen  is  given  off 
and  metallic  sodium  again  remains. 

With  Potassium. — If  the  metal  potassium  is  heated 
in  the  presence  of  hydrogen,  a  hydride  is  formed  : — 

4K.  +  H2  =  K.4H2. 

This  hydride  has  the  same  characteristic  reaction  with 

3 


34  HYDROGEN 

water,   but  it  has  a  distinctive  reaction,  in  that  on  ex- 
posure to  air  it  catches  fire  :  — 

2K4H2  +  9O2  =  4K2O4  +  2H2O. 


With  Magnesium*  —  If  hydrogen  is  passed  over  hot 
metallic  magnesium  the  hydrogen  is  absorbed  :  — 

Mg  +  H2  =  MgH2. 

This  hydride  is  decomposed  with  water,  with  the  pro- 
duction of  magnesium  hydrate  and  hydrogen  :— 
MgH2  +  2H2O  =  Mg(OH)2  +  2H2. 

With  Calcium*  —  If  hydrogen  is  passed  over  hot 
metallic  calcium  the  hydrogen  is  absorbed  :— 

Ca  +  H2  =  CaH2. 

The  hydride  is  decomposed  by  water,  according  to  the 
equation— 

CaH2  +  2H20  =  Ca(OH)2  +  2H2. 

Calcium  hydride,  unlike  the  metallic  hydrides  already 
mentioned,  is  a  commercial  possibility,  and  under  the 
name  of  "Hydrolith"  has  been  used  by  the  French 
Army  in  the  field  for  the  inflation  of  observation 
balloons.  Its  use  for  this  purpose  is  governed  by  French 
patent  No.  327878,  1902,  in  the  name  of  Jaubert. 

With  Cerium.  —  If  hydrogen  is  passed  over  hot 
metallic  cerium  the  hydrogen  is  absorbed  :  — 

Ce  +  H2  =  CeH2. 

This  hydride  is  decomposed  with  water  in  the  same 
manner  as  calcium  hydride,  but  as  a  source  of  hydrogen 
it  is  far  too  rare  to  be  employed. 

However,  if  an  alloy  of  cerium  with  magnesium  and 


CHEMICAL  PROPERTIES  # 

aluminium  is  heated  below  its  melting  point  in  a  stream 
of  hydrogen,  the  latter  is  absorbed,  with  the  formation 
of  cerium  hydride  within  the  alloy,  which,  after  cooling, 
possesses  to  a  remarkable  degree  the  property  of  emit- 
ting sparks  when  rubbed  with  any  rough  surface. 
These  sparks  are  sufficiently  hot  to  ignite  coal  gas  and 
petrol  vapour,  hence  the  employment  of  this  hydrogen- 
ated  alloy  in  the  patent  lighters  which  have  of  recent 
years  become  so  common  in  this  country. 

Chemical  Combination  of   Hydrogen  with    Animal 
and  Vegetable  Oil. 

Owing  to  the  discoveries  of  M.  Sabatier  a  new 
use  has  been  found  for  hydrogen,  and  a  vast  and  ever- 
growing industry  created,  known  as  "  fat  hardening  ". 

The  chief  uses  for  animal  and  vegetable  fats  are  for 
the  making  of  candles,  soap,  and  edible  fats  such  as  are 
incorporated  in  butter  substitutes,  sold  generically  under 
the  name  of  "  Margarine  ". 

Animal  and  vegetable  fats  are  generally  mixtures  of 
a  certain  number  of  complicated  organic  chemical  com- 
pounds, amongst  the  chief  of  which  may  be  mentioned 
linolein,  olein,  stearin,  and  palmitin.  The  physical 
properties  of  these  compounds  are  somewhat  different. 
Thus,  those  containing  considerable  proportions  of 
stearin  and  palmitin  are  usually  solid  at  atmospheric 
temperature,  while  those  in  which  the  chief  constituent 
is  either  linolein  or  olein  are  liquids  at  such  temperature. 

These  chemical  compounds — linolein,  olein,  stearin, 
and  palmitin — are  what  are  known  as  "  glycerides," 
i.e.  they  are  compounds  of  glycerine  with  an  organic 
acid. 


36  HYDROGEN 

Now  since  glycerine  is  of  great  value  in  a  variety  of 
ways,  chiefly  for  the  production  of  nitro-glycerine,  it  is 
customary  to  split  these  glycerides  up  into  glycerine  and 
their  organic  acid  before  indulging  in  any  other  process. 
This  may  be  accomplished  by  the  use  of  superheated 
steam.  Thus,  when  such  steam  is  blown  through  pal- 
mitin  the  following  reaction  takes  place  : — 

QH5(C16H3102)3  +  3H20  =  3H(C16H3102)  +  C3H5(HO)3. 

Palmitin  Steam  Palmitic  acid  Glycerine 

Or  through  olein  :— 

C3H6(C18H8803)3  +  3H20  =  3H(C18H3302)  +  C3H5(HO)3. 

Olein  Steam  Oleic  acid  Glycerine 

The  physical  properties  of  these  organic  acids  are 
very  interesting  and  important.  Their  melting  points 
are  : — * 

Palmitic  acid          .         .         .         Melting  point,  62 '6°  C. 
Stearic  acid    .         .         .         .  ,,  „       69 '3°  C. 

Oleic  acid     .         .         .         .  ,,  „       i4'o°  C. 

Now  this  oleic  acid,  owing  to  its  low  melting  point, 
is  not  of  great  value,  as  it  cannot  be  used  for  candles. 
However,  the  discoveries  of  M.  Sabatier  have  shown 
that  under  certain  conditions  of  temperature  and  in 
the  presence  of  nickel  or  cobalt  (which  themselves 
undergo  no  permanent  change),  the  low  melting  linoleic 
and  oleic  acids  may  be  converted  into  stearic  acid  by 
the  introduction  of  hydrogen  into  the  liquid  organic 
acid.  Thus  :— 

C17H33COOH  +  H2  =  C17H35COOH. 
Oleic  acid  Stearic  acid 

The  nickel  in  this  process  may  be  introduced  into 
the  liquid  organic  acid  by  merely  adding  spongy  nickel 
to  the  molten  oleic  acid  ;  or  as  a  volatile  compound 


CHEMICAL  PROPERTIES  37 

known  as  "  Nickel  Carbonyl  "  it  may  be  blown  in  to- 
gether with  the  hydrogen. 

In  either  case,  for  the  conversion  of  the  linoleic  and 
oleic  acids  into  stearic  acid,  the  temperature  of  the  acids 
should  be  between  200°  and  220°  C.  When  the  nickel 
is  introduced,  in  the  form  of  carbonyl,  at  the  same  time 
as  the  hydrogen,  the  carbonyl  is  decomposed  into  metal- 
lic nickel  and  carbon  monoxide — the  latter  taking  no 
part  whatever  in  the  reaction  and  being  available  for 
the  production  of  further  nickel  carbonyl. 

The  nickel  which  is  used  in  this  process  performs 
merely  a  catalytic  function  and  does  not  of  itself  under- 
go permanent  change.  However,  its  catalytic  property 
may  be  destroyed  either  by  the  method  by  which  it  is 
prepared  or  by  certain  impurities  in  the  hydrogen  with 
which  the  hydrogenation  is  carried  out.  While  it  is  not 
important  that  the  hydrogen  should  be  very  pure — in 
fact,  it  may  contain  carbon  monoxide,  nitrogen,  carbon 
dioxide,  and  methane — it  is  absolutely  essential  that  it 
should  be  entirely  free  from  sulphur  dioxide,  sulphuretted 
hydrogen,  and  other  sulphur  compounds,  bromine, 
chlorine,  iodine,  hydrochloric  acid,  arsenuretted  hydro- 
gen, selenuretted  hydrogen,  and  teluretted  hydrogen. 

If  the  nickel  is  introduced  into  the  fatty  acid  in  the 
solid  form  it  is  important  that  it  should  be  absolutely 
free  from  sulphur,  selenium,  tellurium,  arsenic,  chlorine, 
iodine,  bromine.  Further,  it  is  important  that  the  nickel 
should  have  been  prepared  by  the  reduction  of  the  oxide 
at  a  temperature  not  exceeding  300°  C.,  and  should  not 
have  been  long  exposed  to  the  air  prior  to  its  use. 

The  weight  of  nickel  used  is  about  o'i  part  to  100 
parts  of  oil  or  fatty  acid  ;  however,  larger  quantities  do 
no  harm.  After  the  hydrogenation  of  the  fatty  acid  or 


38  HYDROQEN 

oil,  practically  the  whole  of  the  nickel  is  recovered  by 
merely  filtering  the  hot  oil  or  fatty  acid. 

In  this  note  the  use  of  hydrogen  in  the  fat  harden- 
ing industry  has  been  described  with  particular  refer- 
ence to  the  conversion  of  the  unsaturated  oleic  and 
linoleic  fatty  acids  into  stearic  acid.  However,  what 
has  been  said  in  regard  to  this  matter  is  equally  appli- 
cable to  the  conversion  of  olein  and  linolein  into  stearin, 
cotton-seed  and  most  fish  oils  being  quite  easily  con- 
verted into  solid  fats. 


CHAPTER  III. 

THE  MANUFACTURE  OF  HYDROGEN. 
CHEMICAL  METHODS. 

THE  PRODUCTION  OF  HYDROGEN. 

WHILE  all  the  processes  described  yield  hydrogen, 
some  are  of  merely  laboratory  use,  others  of  commercial 
use,  and  yet  others  of  use  for  the  generation  of  hydro- 
gen for  war  purposes,  under  conditions  where  rapidity 
of  production  and  low  weight  of  reagents  are  more  im- 
portant than  the  cost  of  the  final  product. 

Where  hydrogen  is  wanted  for  commercial  purposes, 
two  types  of  process  will  generally  be  found  most  use- 
ful :  the  electrolytic,  where  not  more  than  1000  cubic 
feet  of  hydrogen  are  required  per  hour  and  conditions 
are  such  that  the  oxygen  produced  can  be  either  ad- 
vantageously used  or  sold  locally  ;  the  Iron  Contact 
process,  the  Linde-Frank-Caro  process,  or  the  Badische 
Anilin  Catalytic  process,  where  yields  of  3000  and  more 
cubic  feet  are  required  per  hour.  However,  local  con- 
ditions and  the  requirements  of  a  particular  trade  may 
make  some  of  the  other  processes  the  more  desirable. 

For  war  hydrogen  may  be  economically  produced  at 
a  base,  and  used  there  for  the  inflation  of  airships,  or 
the  filling  of  high-pressure  bottles  for  transport  to  the 
Kite  Balloon  Sections  in  the  field.  Where  transport  con- 
ditions are  difficult  it  may  be  advantageous  to  generate 

(39) 


40  MANUFACTURE  OF   HYDROGEN 

the  hydrogen  on  the  field  at  the  place  where  it  will 
be  used  ;  then,  probably,  the  Silicol,  Hydrogenite  or 
Hydrolith  processes  will  have  the  advantage,  but  here 
again  it  is  not  possible  to  speak  with  any  great  precision, 
as  local  conditions,  even  in  war,  must  have  great  in- 
fluence on  the  selection  of  the  most  suitable  process. 
The  production  of  hydrogen  can  be  accomplished 
by  a  large  variety  of  methods,  which  may  be  divided 
into  two  main  classes,  viz.  chemical  and  physical,  while 
there  is  an  intermediate  class  in  which  the  production 
of  hydrogen  is  accomplished  in  two  stages,  one  being 
chemical  and  the  other  physical. 

CHEMICAL  METHODS  OF  PRODUCING  HYDROGEN. 

The  chemical  methods  of  producing  hydrogen  may 
be  divided  into  four  classes  : — 

1.  Methods  using  an  acid. 

2.  Methods  using  an  alkali. 

3.  Methods  in  which  the  hydrogen  is  derived  from 
water. 

4.  Methods  in  which  the  hydrogen  is  produced  by 
methods  other  than  the  above. 

(i)  Methods  Using  an  Acid. 

With  Iron* — If  dilute  sulphuric  acid  is  brought  into 
contact  with  iron,  chemical  action  takes  place,  with  the 
production  of  hydrogen  and  ferrous  sulphate,  in  accord- 
ance with  the  following  equation  : — 

Fe  +  H2S04  =  H2  +  FeS04. 

Theoretically,  to  produce  1000  cubic  feet  of  hydrogen 
at  30  inches  barometric  pressure  and  40°  F.  by  this  pro- 
cess, 1 55  Ib.  of  iron  and  272  Ib.  of  pure  sulphuric  acid  are 


CHEMICAL    METHODS  41 

required,  or  a  total  weight  of  pure  reagents  equal  to 
427  Ib.  per  1000  cubic  feet  of  hydrogen  produced.  From 
the  figures  given  above,  the  approximate  cost  of  material 
per  i  ooo  cubic  feet  of  hydrogen  can  be  calculated  if  the 
prevailing  prices  of  iron  and  sulphuric  acid  are  known. 
Of  course,  pure  sulphuric  acid 'is  not  an  essential  for  the 
process,  but  allowance  for  the  impurity  of  the  sulphuric 
acid  and  iron  must  be  made  in  any  calculation  for  cost 
or  weight. 

The  hydrogen  produced  by  this  method  varies  con- 
siderably in  purity.  It  is  liable  to  contain  methane  to 
an  extent  which  depends  on  the  carbon  content  of  the 
iron  ;  it  may  also  contain  phosphine,  depending  on  the 
phosphorus  content  of  the  iron,  sulphuretted  hydrogen, 
depending  on  the  sulphur  content  of  the  iron,  and  traces 
of  silicon  hydride,  depending  on  the  silicon  content  of 
the  iron.  It  is  also  liable  to  contain  arsine  or  arsenu- 
retted  hydrogen,  depending  on  the  arsenic  content  of 
the  sulphuric  acid,  the  commercial  acid  frequently  con- 
taining considerable  amounts  of  this  impurity.  Unless 
specially  treated,  the  hydrogen  produced  is  always  acid, 
and  therefore  unsuitable  for  balloon  and  airship  pur- 
poses. 

The  impure  gas  produced  by  this  method  may  be 
purified  by  being  passed  through  or  scrubbed  by  water  ; 
this  will  remove  much  of  the  acid  carried  by  the  gas, 
dust,  and  some  of  the  methane,  phosphine,  arsine,  and 
sulphuretted  hydrogen.  If  after  this  treatment  the  gas 
is  passed  through  a  solution  of  a  lead  salt,  the  remain- 
ing acidity  and  sulphuretted  hydrogen  can  be  removed. 
This  method  of  the  treatment  of  the  impure  gas  is 
covered  by  English  patent  16277,  1896,  in  the  names  of 
Pratis  and  Marengo.  Further  patents  in  connection 


42  MANUFACTURE  OF   HYDROGEN 

with  this  method  of  producing  hydrogen  have  been 
taken  out  by  Williams  (English  patent  8895,  1886), 
Hawkins  (English  patent  15379,  1891),  Pratis  and 
Marengo  (English  patent  15509,  1897),  Hawkins 
(English  patent  25084,  1897),  an<^  Fielding  (English 
patent  17516,  1898). 

With  Zinc* — If  dilute  sulphuric  acid  is  brought  into 
contact  with  zinc,  chemical  action  takes  place,  with  the 
production  of  zinc  sulphate  and  hydrogen,  in  accordance 
with  the  following  equation  : — 

Zn  +  H2SO4  =  H2  +  ZnSO4. 

Theoretically,  to  produce  1000  cubic  feet  of  hydrogen 
at  30  inches  barometric  pressure  and  40°  F.  by  this  pro- 
cess, 1 80  Ib.  of  zinc  and  272  Ib.  of  pure  sulphuric  acid 
are  required,  or  a  total  weight  of  pure  reagents  equal  to 
452  Ib.  per  1000  cubic  feet  of  hydrogen  produced. 

The  hydrogen  produced  by  this  process  is  liable  to 
fewer  impurities  than  when  iron  is  used,  but  it  is  always 
acid  and  liable  to  contain  arsine  if  commercial  sulphuric 
acid  is  used. 

The  zinc  sulphate  produced  in  this  process  can  be 
turned  more  easily  to  commercial  account  than  iron 
sulphate.  If  to  the  solution  of  the  zinc  sulphate  result- 
ing from  the  process  sodium  carbonate  or  sodium 
hydrogen  carbonate  is  added,  a  precipitate  of  hydrated 
zinc  basic  carbonate  or  zinc  carbonate  is  obtained,  which 
on  ignition  in  a  furnace  yields  zinc  oxide  (commercially 
known  as  "zinc  white"),  water,  and  carbon  dioxide. 
Zinc  white  has  a  commercial  value  as  a  basis  or  body 
ln  paints  ;  it  has  one  great  advantage  over  white  lead, 
which  is  used  for  the  same  purpose,  in  that  it  is  far  less 
poisonous.  This  method  of  treatment  of  the  residual 


CHEMICAL   METHODS  43 

zinc  sulphate  is  the  subject  of  a  patent  by  Barton 
(English  patent  28534,  1910). 

The  previous  list  of  patents  for  the  reaction  of  iron 
and  sulphuric  acid  also  cover  the  use  of  zinc  and 
sulphuric  acid  for  the  production  of  hydrogen. 

There  are  other  metals  which  will  yield  hydrogen 
with  sulphuric  acid,  such  as  cadmium  and  nickel,  while 
many  metals  will  yield  hydrogen  with  hydrochloric  acid, 
such  as  tin,  nickel,  and  aluminium.  However,  these 
reactions  cannot  be  regarded  as  commercial  means  of 
producing  hydrogen. 

(2)  Methods  Using  an  Alkali. 

With  Zinc. — If  a  solution  of  caustic  soda  in  water 
is  brought  into  contact  with  metallic  zinc,  chemical 
reaction  takes  place,  with  the  production  of  sodium 
zincate  and  hydrogen.  The  reaction  is  expressed  in 
the  following  equation  : — 

Zn  +  2NaOH  =  H2  +  Na2ZnO2. 

Theoretically,  to  produce  1000  cubic  feet  of  hydro- 
gen at  30  inches  barometric  pressure  and  40°  F.,  180  Ib. 
of  zinc  and  224  Ib.  of  pure  caustic  soda  are  required,  or  a 
total  weight  of  pure  reagents  equal  to  404  Ib.  per  1000 
cubic  feet  of  hydrogen  produced. 

The  hydrogen  produced  by  this  process  is  generally 
very  pure,  but,  depending  on  the  purity  of  the  zinc,  it  is 
liable  to  contain  arsine.  As  the  gas  is  alkaline,  owing 
to  the  caustic  soda  carried  in  suspension,  it  requires  to 
be  scrubbed  to  make  it  suitable  for  balloons  and  air- 
ships. 

A  modification  of  this  process  has  been  the  subject 
of  a  patent.  Zinc  as  a  fine  powder  is  mixed  with  dry 


44  MANUFACTURE  OF   HYDROGEN 

slaked  lime  ;  then  when  hydrogen  is  required,  the  mix- 
ture is  heated  in  a  retort  and  hydrogen  is  evolved,  the 
reaction  being  expressed  : — 

Zn  +  Ca(OH)2  =  H2  +  CaZnO2. 

In  this  modification  of  the  process  to  produce  1000 
cubic  feet  of  hydrogen  at  30  inches  barometric  pressure 
and  40°  F.,  180  Ib.  of  zinc  and  207  Ib.  of  slaked  lime 
are  required,  or  a  total  weight  of  pure  reagents  equal  to 
387  Ib.  per  1000  cubic  feet  of  hydrogen  produced. 

By  the  substitution  of  magnesium  hydroxide  instead 
of  slaked  lime  a  similar  reaction  takes  place,  but  the 
total  weight  per  1000  cubic  feet  of  hydrogen  produced 
is  reduced  to  341  Ib. 

This  process,  with  its  modification,  is  covered  by 
a  patent  by  Majert  and  Richter  (English  patent 
4881,  1887),  and  is  primarily  intended  as  a  process  for 
the  generation  of  hydrogen  in  the  field  for  the  inflation 
of  observation  balloons. 

THE  HYDRIK  OR  ALUMINAL  PROCESS. 

With  Aluminium.— If  a  solution  of  caustic  soda  is 
brought  into  contact  with  metallic  aluminium,  chemical 
reaction  takes  place,  with  the  production  of  sodium 
aluminate  and  hydrogen,  in  accordance  with  the  follow- 
ing equation  :— 

2A1  +  6NaOH  =  3H2  +  2Al(ONa)3. 

Theoretically,  to  produce  1000  cubic  feet  of  hydrogen 
at  30  inches  barometric  pressure  and  40°  F.,  50  Ib.  of 
aluminium  and  225  Ib.  of  pure  caustic  soda  are  required, 
or  a  total  weight  of  pure  reagents  equal  to  275  Ib.  per 
1000  cubic  feet  of  hydrogen. 

The  hydrogen  produced  by  this  process  is  generally 


CHEMICAL    METHODS  45 

very  pure,  but  the  gas  is  frequently  alkaline  from  minute 
traces  of  caustic  soda  carried  in  suspension,  which  must 
be  removed  by  scrubbing  with  water  before  the  hydrogen 
is  suitable  for  balloons  and  airships. 

THE  SILICOL  PROCESS. 

With  Silicon. — If  a  solution  of  caustic  soda  is  brought 
into  contact  with  elemental  silicon,  chemical  reaction 
takes  place,  with  the  production  of  sodium  silicate  and 
hydrogen.  The  following  equation  was  supposed  to 
represent  the  reaction  :— 

Si  +  2NaOH  +  H20  =  Na2SiO3  +  2H2. 

Theoretically,  to  produce  1000  cubic  feet  of  hydrogen 
at  30  inches  barometric  pressure  and  40°  F.,  38*8  Ib.  of 
silicon  and  1 1 1  Ib.  of  pure  caustic  soda  are  required,  or 
a  total  weight  of  pure  reagents  equal  to  149*8  Ib.  per 
1000  cubic  feet  of  hydrogen. 

The  gas  produced  by  this  process  is  singularly  pure, 
generally  containing  99*9  per  cent,  hydrogen  by  volume 
(if  the  water  vapour  is  removed  before  analysis),  '01  per 
cent,  of  arsine  and  phosphine,  "005  per  cent,  acetylene, 
the  remaining  impurity  being  air,  which  is  introduced 
in  the  powdered  silicon  and  also  in  solution  in  the 
water. 

In  working  this  process  practically,  pure  silicon  is 
not  used,  high-grade  ferro-silicon,  containing  82-92  per 
cent,  silicon,  being  employed.  As  will  be  seen  from  the 
above  equation,  theoretically  2*86  parts  of  anhydrous 
caustic  soda  by  weight  should  be  used  for  one  part  of 
silicon.  However,  in  working  in  practice,  one  part  of 
pure  silicon  and  1 7  parts  of  pure  caustic  soda  are  em- 
ployed. This  discrepancy  between  the  theoretical 


46  MANUFACTURE  OF   HYDROGEN 

quantity  of  soda  and  that  actually  used  has  been  investi- 
gated by  the  author,  who  originally  considered  that  the 
following  reaction  might  be  taking  place  : — 

Si  +  2H2O  =  SiO2  +  2H2. 

That  is  to  say,  the  silicon  was  being  oxidised  by  the 
oxygen  of  the  water,  and  hydrogen  liberated. 

The  first  experiment  performed  was  the  heating  of 
the  ferro-silicon  l  (92  per  cent.  Si)  in  a  flask  with  boiling 
water ;  the  resulting  steam  was  condensed,  but  there 
was  no  residual  gas.  Therefore  it  was  concluded  that 
at  the  temperature  of  boiling  water  no  reaction  between 
ferro-silicon  and  water  took  place. 

Remembering  that  the  temperature  of  the  caustic 
soda  solution  used  in  the  silicol  process  is  above  100  C., 
frequently  rising  to  120°  C.,  it  was  thought  that  a  higher 
temperature  might  perhaps  produce  the  suspected  re- 
action ;  ferro-silicon  was  accordingly  heated  in  an  at- 
mosphere of  steam  in  an  electric  resistance  furnace  to 
a  temperature  of  300°  C.,  but  still  no  hydrogen  was 
produced.  Consequently  it  was  concluded  that  the  ex- 
planation of  the  smaller  consumption  of  caustic  soda  than 
would  be  anticipated  from  theoretical  considerations  must 
be  explained  on  some  basis  other  than  the  reaction  of 
silicon  with  water. 

The  next  experiment  attempted  was  the  heating  of 
ferro-silicon  with  sodium  silicate,  i.e.  with  a  pure  form  of 
the  product  of  the  usual  equation.  When  ferro-silicon 
was  heated  with  an  aqueous  solution  of  pure  sodium 
mono-silicate,  considerable  quantities  of  hydrogen  were 

1  The  ferro-silicon  employed  was  of  French  manufacture.  I  have 
since  found  that  some  high-grade  Canadian  ferro-silicons  give  traces 
of  hydrogen  with  water  under  the  conditions  cited  in  the  experiments. 


CHEMICAL    METHODS  47 

evolved,  thus  warranting  the  conclusion  that  the  ordinary 
equation — 

Si  +  2NaOH  +  H2O  =  Na2SiO3  +  2H2 

is  not  entirely  correct,  and  that  a  silicate  richer  in  silica 
than  that  indicated  in  the  equation  was  formed,  and  that 
probably  the  following  reaction  proceeds  to  some  ex- 
tent :— 

Si  +  Na2SiO3  +  2H2O  =  Na2Si2O5  +  2H2. 

Assuming  this  second  reaction  to  take  place  at  the 
same  time  as  the  first,  the  reaction  can  be  expressed  : — 
2Si  +  2NaOH  +  3H2O  =  Na2Si2O5  +  4H2, 

which  is  equivalent  to  1000  cubic  feet  of  hydrogen  at 
30  inches  barometric  pressure  and  40°  F.  being  produced 
by  38*8  Ib.  of  silicon  and  55*5  Ib.  of  caustic  soda,  the 
ratio  of  pure  caustic  soda  to  pure  silicon  being  as  i  "43 
is  to  i. 

Using  a  plant  producing  about  30,000  cubic  feet  of 
hydrogen  per  hour,  it  was  found  that  i  '9  parts  of  caustic 
soda  (76  per  cent.  NaOH)  to  i  part  of  Canadian  ferro- 
silicon  (84  per  cent.  Si)  gave  very  satisfactory  results, 
the  ratio  of  the  pure  reagents  being  as  1*72  parts  of 
caustic  soda  by  weight  to  i  part  of  silicon. 

Theoretically,  22*5  cubic  feet  of  hydrogen  should  have 
been  produced  per  Ib.  of  the  commercial  ferro-silicon 
used,  but  in  practice  it  was  found  that  20*7  cubic  feet  were 
obtained,  the  discrepancy  of  i  *8  cubic  feet  being  to  some 
extent  accounted  for  by  the  protective  action  of  impurities, 
loss  through  leaks  and  also  by  hydrogen  being  mechani- 
cally carried  away  by  the  water  used  for  cooling  the 
issuing  hydrogen. 

Description  of  Silicol  Plant. — The  essentials  of  a 
silicol  plant  are  shown  in  the  diagram  (Fig.  3).  The 


48 


MANUFACTURE  OF   HYDROGEN 


requisite  quantity  of  caustic  soda  is  placed  in  the  tank 
on  the  right  and  the  necessary  water  added  to  it  to  make 
a  25  per  cent,  solution.  To  assist  solution  there  is  a 


stirrer  in  this  tank,  which,  in  small  plants,  is  hand-oper- 
ated and  in  large  ones  power-operated.  When  the  whole 
of  the  caustic  soda  has  gone  into  solution,  which  it  readily 


CHEMICAL    METHODS  49 

does  as  a  result  of  the  heat  of  solution  and  the  stirring, 
the  valve  D  is  opened,  allowing  the  whole  of  the  soda 
solution  to  run  via  the  pipe  E  into  the  generator.  When 
the  solution  has  run  from  the  caustic  soda  tank  into  the 
generator  the  valve  D  is  closed,  then  the  necessary 
quantity  of  ferro-silicon  is  placed  in  the  hopper  on  the 
top  of  the  generator  and  the  lid  of  the  hopper  closed, 
making  a  gas-tight  joint.  In  small  plants  a  little  mineral 
grease  is  added  to  the  generator,  via  the  grease  box. 

The  plant  is  then  ready  for  operation,  and  silicol  is 
cautiously  fed  into  the  generator  by  means  of  the  hand- 
operated  feed  worked  from  F. 

During  the  generation  the  fluid  charge  in  the  gene- 
rator is  kept  stirred  by  means  of  the  stirring  mechanism 
worked  from  G.  The  hydrogen  produced  passes  through 
the  tube  condenser  (where  it  is  cooled  and  thus  freed 
from  steam)  and  then  on  to  the  gas  holder. 

An  excessive  pressure,  due  to  rapid  generation  of 
hydrogen,  is  guarded  against  by  means  of  a  water  seal 
as  shown. 

When  generation  is  complete,  the  resulting  sodium 
silicate  solution  is  rapidly  run  out  via  the  trapped  dis- 
charge pipe  and  the  interior  of  the  generator  washed 
with  cold  water  supplied  from  the  tap  B.  Thermometers 
at  Ti,  T2,  T3,  and  T4  enable  the  temperature  at  dif- 
ferent parts  of  the  apparatus  to  be  observed  and,  if 
necessary,  controlled. 

The  description  of  the  apparatus  has,  of  necessity,  to 
be  somewhat  general,  as  these  plants  are  made  in  sizes 
varying  from  150x3  to  60,000  cubic  feet  per  hour  produc- 
tion and  consequently  differ  in  detail ;  thus,  in  large 
plants,  the  tube  condenser  is  not  employed  and  the  hot 
hydrogen  passes  up  a  tower  packed  with  coke,  down 

4 


50  MANUFACTURE  OF  HYDROGEN 

which  water  is  falling.  Further,  in  large  plants,  the 
generator  itself  is  water-jacketed,  as  the  heat  of  chemical 
reaction  would  otherwise  be  excessive. 

The  silicol  process  has  the  advantage  of  giving  a 
very  great  hydrogen  production  per  hour  from  a  plant 
of  small  cost — its  disadvantage  is  that  at  the  pre- 
vailing cost  of  the  reagents  employed  the  hydrogen  is 
expensive. 

To  sum  up,  this  process  is  exceedingly  useful  where 
large  quantities  of  hydrogen  are  from  time  to  time 
required,  but  it  is  not  the  best  process  to  use  where 
there  is  a  constant  hour-to-hour  demand  for  hydrogen. 

The  Silicon  Content  of  the  Fem>Silicon. — The 
grade  of  ferro-silicon  used  in  this  process  is  very  import- 
ant, as  low-grade  material  does  not  yield  anything  like 
the  theoretical  quantity  of  hydrogen  which  should  be 
obtained  from  the  silicol  present.  This  arises  to  a  slight 
extent  from  the  protective  action  of  the  impurities,  which 
enclose  particles  of  silicon  and  therefore  prevent  the 
caustic  soda  from  attacking  it. 

The  curve  (Fig.  4),  obtained  experimentally,  shows 
that  to  get  even  moderate  efficiency  ferro-silicon  of  over 
80  per  cent,  silicon  content  should  be  used. 

The  Degree  of  Fineness  of  the  Ferro'Silicon.- 

The  degree  of  subdivision  of  the  ferro-silicon  is  also 
important,  not  so  much  because  of  its  effect  on  the  total 
yield  of  hydrogen,  but  because  of  its  influence  on  the 
rapidity  of  generation. 

Fig.  5  indicates  the  speed  of  evolution  of  hydrogen 
from  two  samples  of  the  same  material,  under  identical 
conditions,  except  that  one  sample  was  much  coarser 
than  the  other. 


CHEMICAL    METHODS 


Hydrogen  Yield  (Litres  per  Gram  of  Ferrosilicon 

0  OOGt-^-'^^t- 
O  fco  ,£.  ch  CD  O  t>>  4*  O>  0 

Relation  of  Silicol  Content 
to  Hydrogen  Yield. 

/ 

4 

J\ 

$/ 

X 

f 

£-\ 

& 

X 

^ 

/ 

•V 

f 

/ 

x 

/ 

7 

x 

7 

1 

,  X 

/ 

X 

•K-^ 

x^ 

3        10       20      30       40       50       60       70       80       90      100% 
Silicon  in  Ferrosilicon. 

FIG.  4. 


l& 

10 

i: 
I: 

8  5 

i 

0 

b 

y 

^ 

^^- 

,  *"^ 

-^  — 

- 

—  • 

*-^- 

—1         • 

^—  - 

—  —  — 

• 

^~~  — 

--  —  r~t 

_ 

^-      — 

:  —  .  ' 

x 

•^ 

/ 

* 

vl$ 

fl?_ 

X 

/ 

fi 

/ 

/ 

/ 

/ 

/ 

, 
/ 

Evolution  of  Hydrogen  from 
88%  Ferrosi'licon,  20-30  Mesh 
and  same  Material  ground  to 
pass  100  Mesh. 

/ 

L 

0        2.4        6        6        10       12       14       16       18      20      2Z       24      26      28      3C 

7>'/77e  />?  Minutes. 

FIG.  5. 


52  MANUFACTURE  OF  HYDROGEN 

The  Strength  of  the  Caustic  Soda. — The  strength 
of  the  caustic  soda  is  very  important  in  this  process.  If 
the  solution  is  too  dilute,  a  very  poor  yield  of  hydrogen 
is  obtained,  and  also  another  difficulty  is  introduced. 
When  the  caustic  soda  solution  is  very  weak,  on  the 
introduction  of  the  ferro-silicon  or  "  silicol "  reaction  takes 
place,  but  the  whole  solution  froths  violently,  the  froth 
being  carried  along  the  pipes  from  the  generator,  causing 
trouble  to  be  experienced  in  the  valves,  and  tending  to 
ultimately  block  the  pipes  themselves.  On  the  other 
hand,  the  caustic  soda  solution  may  be  too  strong.  In 
this  case,  before  the  whole  of  the  caustic  soda  has  re- 
acted with  the  requisite  amount  of  silicol,  the  solution 
becomes  either  very  viscous  or  actually  solid,  so  a  poor 
yield  is  obtained  and  the  sludge  cannot  be  got  out  of 
the  generator  without  allowing  it  to  cool  down  and  then 
digging  it  out  by  manual  labour. 

The  following  laboratory  experiments  with  ferro- 
silicon  containing  92  per  cent,  silicon  and  caustic  soda 
containing  98  per  cent,  of  sodium  hydroxide  illustrate  the 
effect  of  soda  solutions  of  varying  strength,  and  also  the 
effect  of  varying  ratios  of  pure  silicon  to  pure  sodium 
hydroxide.  From  these  it  will  be  seen  that  the  most 
economical  results  are  obtained  when  a  40  per  cent, 
solution  of  caustic  soda  is  employed  and  the  ratio  of 
silicon  to  sodium  hydroxide  is  approximately  -i  to  i  '6. 

In  practice  such  strong  solutions  are  not  used,  as, 
owing  to  the  evaporation  of  a  good  deal  of  the  water 
during  the  process,  towards  the  end  a  degree  of  concen- 
tration would  be  reached  which  would  prevent  the 
sludge  from  being  run  out  of  the  plant.  A  solution  con- 
taining about  25  per  cent,  of  caustic  soda  is  found  to 
give  in  practice  very  satisfactory  results.  Such  a  solu- 


CHEMICAL    METHODS 


53 


tion  of  commercial  caustic  soda,  containing  about  2  5  per 
cent,  of  pure  sodium  hydrate,  has  at  100°  F.  a  specific 
gravity  of  approximately  1*32 — a  figure  which  is  very 
useful  to  remember,  as  by  means  of  a  hydrometer  a 
rapid  check  can  be  made  of  the  caustic  soda  solution 
being  prepared  for  use  in  the  process. 

The  ratio  of  silicol  to  caustic  soda  should  be  such 
that  the  ratio  of  pure  silicon  to  pure  sodium  hydrate  is 
as  i  to  172,  but  this  figure  is  capable  of  modification 
to  a  slight  extent,  depending  on  the  temperature  of  the 
mixture,  which  is  naturally  higher  in  large  plants  than 
in  small  ones. 


Experiment. 

Strength  of  Soda 
Solution. 

Ratio  of  Silicon 
to  pure  Caustic 
Soda. 

Yield  in  Cubic  Feet  per  Ib. 
of  Silicol. 
1  (At  30"  Bar.  and  60°  F.). 

I 

10  per  cent. 

T  to  0745 

13-62 

2 

10 

i        1*065 

14*3° 

3 

10 

1-480 

I5'36 

4 

10 

3-200 

16-80 

5 

3° 

0-852 

I9'35 

6 

3° 

2-13 

23-90 

7 

30 

3*19 

23-58 

8 

40 

,    1-58 

24*10 

9 

40 

i»  3'I9 

24-50 

The  Use  of  Slaked  Lime  instead  of  Caustic  Soda. 
— The  experiments  already  described  indicate  that  to 
obtain  hydrogen  from  ferro-silicon  a  base  must  be  used 
to  react  with  it.  It  therefore  occurred  to  the  author 
that  the  cost  of  the  operation  of  the  process  might  be 
reduced  by  the  substitution  of  slaked  lime  for  caustic 
soda. 

1  Theoretically  the  maximum  possible  yield  under  these  condi- 
tions of  temperature  and  pressure  would  be  25-4  cubic  feet  per  Ib.  of 
silicol  of  this  purity. 


54  MANUFACTURE  OF   HYDROGEN 

Laboratory  experiments,  using  ferro-silicon  contain- 
ing 92  per  cent,  silicon  and  pure  slaked  lime,  were  made 
to  see  if  the  following  reaction  took  place  : — 
Si  +  Ca(OH)2  +  H2O  =  CaSiO3  +  2H2. 

The  results  of  these  experiments  indicated  that  when 
i  part  of  ferro-silicon,  2*5  parts  of  slaked  lime,  and 
10  parts  of  water  were  used,  a  yield  of  1*53  cubic  feet 
of  hydrogen  was  obtained  per  Ib.  of  ferro-silicon  used. 
Theoretically,  under  the  conditions  of  the  experiment, 
25-4  cubic  feet  should  have  been  produced  per  Ib.  of 
ferro-silicon  ;  consequently  it  can  be  safely  concluded 
that  without  an  external  supply  of  heat  the  suspected 
reaction  only  takes  place  to  a  very  limited  extent. 

Remembering     that    slaked    lime   will    decompose 
sodium    silicate,    producing   caustic   soda   and    calcium 
silicate,  in  accordance  with  the  following  equation  : — 
Na2Si03  +  Ca(OH)2  =  2NaOH  +  CaSiO3, 

it  was  thought  that  the  following  reactions  might  take 
place  if  both  caustic  soda  and  slaked  lime  were  employed 
at  the  same  time  : — 

(1)  281  +  2NaOH  +  3H2O  =  Na2Si2O,  +  4H2. 

(2)  Na2Si2O5  +  Ca(OH)2  =  2NaOH  +  CaSi2O5. 

Since  the  caustic  soda  in  the  solution  would  be  re- 
generated after  it  had  reacted  with  the  silicol,  it  would 
be  available  for  reacting  with  yet  more  silicol,  and  would 
consequently  reduce  the  quantity  of  caustic  soda  used  in 
the  process. 

The  following  experiments,  using  a  mixture  of  slaked 
lime  and  caustic  soda,  appear  to  indicate  that  the  sur- 
mise was  partly  or  wholly  correct,  for  with  approximately 
only  half  as  much  caustic  soda  as  ferro-silicon  a  yield 
of  almost  1 6  cubic  feet  of  hydrogen  per  Ib.  of  ferro- 


CHEMICAL    METHODS 


55 


silicon  was  obtained.  By  contrasting  these  experiments 
with  those  already  given,  using  caustic  soda  alone,  it  will 
be  seen  that  the  yield  obtained  from  the  caustic  soda  is 
much  greater  than  that  which  would  have  been  obtained 
were  no  lime  present.  Whether  in  operating  on  a  large 
scale  equally  good  results  would  be  obtained  has  not  yet 
been  determined.1 


Experiment. 

Ratio  of  Silicon  to 
pure  Caustic  Soda. 

Ratio  of  Silicon 
to  Lime. 

Yield  in  Cubic  Feet 
per  Ib.  of  Silicol  at 
30"  Bar.  and  60°  F. 

I 
2 

3 

I  to  0*426 
I    „  0-426 
I    „  0-426 

I  to  1-52 
I    „   272 
I    »   3*04 

I4-95 
I5'95 
I5'23 

The  Chemical  Composition  of  the  Sludge. — The 

equations  which  have  already  been  given  indicate  that  the 
products  of  this  process  are  hydrogen  and  sodium  disili- 
cate  in  solution  in  water.  Since,  however,  neither  the 
ferro-silicon  nor  caustic  soda  employed  are  pure,  in  the 
practical  production  of  hydrogen  by  this  method,  pro- 
ducts other  than  those  shown  in  the  equations  are  found. 

The  commercial  caustic  soda  employed  always  con- 
tains a  certain  amount  of  carbonate  of  soda,  which  takes 
no  part  in  the  reaction  and  is  found  unaltered  in  the 
sludge.  The  same  remark  applies  to  the  iron  contained 
in  the  ferro-silicon. 

The  following  analysis  gives  the  chemical  composi- 
tion of  the  sludge  produced  when  1414  Ib.  of  ferro- 
silicon,  containing  84  per  cent,  of  silicon,  and  2688  Ib. 

1  Since  the  above  experiments  the  author  has  found  that  there  is 
a  patent  for  the  use  of  lime  in  conjunction  with  caustic  soda  and 
silicon,  which,  under  the  name  of  "  Hydrogenite,"  has  been  employed 
by  the  French  Army  for  inflating  observation  balloons  in  the  field. 


MANUFACTURE  OF   HYDROGEN 


of  caustic  soda,  containing  76  percent,  of  sodium  hydrate, 
was  employed.  Besides  the  sludge  29,300  cubic  feet  of 
hydrogen  was  produced,  measured  at  a  temperature  of 
60°  F.  and  a  barometer  of  30  inches. 


CHEMICAL  COMPOSITION  OF  SLUDGE. 


Moisture     ..... 

Silica 

Sodium  carbonate 

Soda  (Na2O,  other  than  carbonate) 

Insoluble  and  undetermined 


Per  Cent, 
by  Weight. 
.      2774 

•      3679 
6 '04 

20'O8 

9'35 

lOO'OO 


CHEMICAL  COMPOSITION  OF  SODA  SOLUTION  USED. 

Caustic  soda          .......     24-5 

Sodium  carbonate          .         .         .         .         .         .3-0 

Specific  gravity  at  100°  F i'324 

CHEMICAL  COMPOSITION  OF  FERRO-SILICON  USED. 

Silicon 84-0 

Iron 5-9 

Aluminium •  5'3 

Carbon         ........  -2 

Undetermined 3-6 

lOO'O 


SCREEN  l  ANALYSIS  OF 

FERRO-SILICON. 

Grms.       Per  Cent 

Through    20,  on    30     . 

141*5  =   10-28 

3° 

40     . 

85-0  =      6-17 

40 

50     . 

98-0  =      7  'I  i 

So 

60     . 

85-5  =     6-21 

60 

70     . 

.      103-0  =     7-48 

70 

80     . 

117-0  =     8-49 

80 

90     . 

64-0  =     4-64 

90 

100       . 

.      104-0  =     7-55 

100 

120       . 

81-0  =     5-88 

120 

ISO       • 

.     338-0  =  24-55 

150 

200       . 

89-0  =     6*46 

Passing                   200     . 

70-0  =     5-12 

!376'5       99^4 

Standard  I.M.M.  screens. 


CHEMICAL    METHODS  57 

The  Use  of  Mineral  Grease. — To  reduce  the  froth- 
ing and  priming  in  this  process  it  is  customary  to  intro- 
duce a  little  mineral  grease,  which  floats  on  the  surface 
of  the  caustic  soda  solution  and  prevents  the  formation 
of  the  froth  to  a  considerable  extent. 

About  32  Ib.  of  mineral  grease  are  advocated  per 
1000  Ib.  of  silicol  used.  However,  if  the  caustic  soda 
solution  is  strong,  i.e.  about  25  percent,  sodium  hydrate, 
and  the  generator  is  wide,  giving  a  large  surface  and  a 
shallow  depth  to  the  caustic  soda  solution,  no  grease 
need  be  used  at  all. 

Precautions  to  be  Observed. — In  this  process  very 
great  care  must  be  taken  in  the  introduction  of  the  ferro- 
silicon.  When  the  ferro-silicon  is  attacked  by  the 
caustic  soda  large  quantities  of  heat  are  given  out, 
raising  the  temperature  of  the  caustic  soda  solution.  If 
the  caustic  soda  solution  is  cold,  ferro-silicon  can  be 
introduced  into  the  solution  far  more  rapidly  than  it  is 
attacked  by  the  soda  ;  consequently  there  is  likely  to 
exist  an  accumulation  of  ferro-silicon  in  the  solution,  the 
temperature  of  which  is  gradually  rising.  A  certain 
critical  temperature  is  ultimately  reached  when  the  whole 
of  the  accumulated  ferro-silicon  is  almost  instantly  at- 
tacked, with  large  yield  of  hydrogen  and  consequently 
the  production  of  high  pressure  in  the  generator. 
Several  explosions  have  been  caused  in  this  country 
from  this  reason.  While  it  is  impossible  to  give  any 
definite  figures,  in  the  ordinary  commercial  plant  for  the 
production  of  hydrogen  by  this  process  the  ferro-silicon 
should  be  added  in  small  quantities,  with  a  period  of 
waiting  between  each  addition,  until  the  caustic  soda 
solution  reaches  a  temperature  of  about  180°  F.  At 


58  MANUFACTURE  OF    HYDROGEN 

this  temperature,  with  a  25  per  cent,  solution  of  caustic 
soda,  high-grade  ferro-silicon  is  almost  instantly  attacked, 
so  it  can  then  be  added  continuously  at  a  rate  which 
does  not  produce  a  pressure  above  the  working  pressure 
of  the  plant. 

In  plants  for  the  operation  of  this  process  no  red  or 
white  lead  whatever  should  be  used  for  making  joints, 
as  both  these  substances  at  a  comparatively  low  tempera- 
ture are  reduced  to  metallic  lead  by  ferro-silicon,  with 
the  evolution  of  large  quantities  of  heat  and  the  produc- 
tion of  incandescence,  the  reaction  taking  place  with  such 
rapidity  as  to  constitute  almost  an  explosion.  This  can 
be  easily  illustrated  by  making  a  mixture  of  finely 
divided  ferro-silicon  and  dry  red  lead,  in  which  the  ratio 
of  the  two  is  i  part  of  pure  silicon  to  12 '2  parts  of  red 
lead.  If  a  match  or  the  end  of  a  cigarette  is  put  to  this 
mixture  it  goes  off  violently,  with  the  production  of  great 
heat,  in  accordance  with  the  following  equation  :— 

Pb3O4  +  28!  =  3?b  +  2SiO2. 

That  the  temperature  produced  is  exceedingly  high  can 
be  well  illustrated  by  putting,  say,  half  an  ounce  of  an 
intimate  dry  mixture  of  ferro-silicon  and  red  lead,  in 
which  the  proportions  of  the  active  principals  are  as 
indicated  in  the  above  equation,  on  a  sheet  of  thin  alu- 
minium, say  TCT  of  an  inch  thick.  On  putting  a  match 
to  this  mixture  it  will  be  found  a  hole  is  melted  in  the 
aluminium  sheet.1 

All  air  must,  if  possible,  be  excluded  from  the  plant 
prior  to  the  introduction  of  the  caustic  soda,  as  other- 
wise in  the  early  stages  of  generation  of  hydrogen  an 
explosive  mixture  might  arise  which  on  ignition  would 

1  The  melting  point  of  aluminium  is  658°  C. 


CHEMICAL   METHODS  59 

produce  a  dangerous  explosion.  Such  ignition  might 
arise  from  a  spark  produced  from  the  mechanism  inside 
the  generator,  by  ferro-silicon  coming  in  contact  with 
red  lead  which  might  have  been  used  in  making  the 
joints  in  the  plant,  by  incandescence  produced  by  the 
reaction  of  ferro-silicon  with  caustic  soda  itself.  If  an 
intimate  mixture  of  powdered  caustic  soda  is  made  with 
ferro-silicon  in  the  ratio  indicated  in  the  equations  on 
the  silicol  process,  and  this  mixture  is  just  moistened 
with  water,  hydrogen  is  rapidly  evolved  and  the  reacting 
mass  frequently  becomes  incandescent.  Such  conditions 
might  arise  in  a  plant  for  operation  of  this  process,  by 
the  caustic  soda  being  splashed  on  to  some  recess  in 
the  generator,  there  becoming  concentrated,  and  ferro- 
silicon  coming  into  contact  with  this  concentrated 
solution.  It  is  for  this  reason  that  caustic  soda  and 
ferro-silicon  should  never  be  stored  in  close  proximity 
to  each  other,  as  this  dangerous  reaction  may  arise  from 
the  breaking  of  drums  containing  the  two  reagents. 

Since  this  process  is  generally  operated  in  conjunc- 
tion with  a  gas-holder,  the  most  easy  way  to  exclude  air 
is  to  allow  hydrogen  from  the  gas-holder  to  blow  back 
through  the  plant  prior  to  putting  this  in  operation. 
Hydrogen  equal  to  about  four  times  the  volume  of  the 
plant  is  required  to  thoroughly  exclude  the  air. 

The  following  patents  with  regard  to  this  process  are 
in  existence  : — 

Consort.  Elektrochem.  Ind. — English  patent  21032, 
September  i4th,  1909. 

French  patent  418946,  July  i8th,  1910. 

English  patent  11640,  May  I3th,  1911. 

Jaubert — French  patent  430302,  August  6th,  1910. 


60  MANUFACTURE  OF   HYDROGEN 

THE  HYDROGEN ITE  PROCESS. 

There  is  a  modification  of  this  method  known  as  the 
hydrogenite  process  whereby  the  use  of  an  aqueous 
solution  of  caustic  soda  is  avoided. 

An  intimate  mixture  of  ferro-silicon  and  powdered 
caustic  soda  or  lime  is  packed  in  strong  cylinders  com- 
municating with  a  high  pressure  storage.  By  means  of 
a  fuse  the  temperature  is  locally  raised  so  that  chemical 
reaction  takes  place,  with  the  production  of  hydrogen 
and  sodium  and  calcium  silicates. 

This  modification  is  covered  by  Jaubert,  English 
patent  422296,  1910;  English  patent  153,  1911. 

With  Carbon. —  If  caustic  soda  is  heated  to  dull 
redness  with  charcoal  or  anthracite  or  some  other  form 
of  pure  carbon,  hydrogen  is  evolved  and  sodium  carbon- 
ate and  sodium  oxide  produced,  in  accordance  with  the 
following  equation  : — 

4NaOH  +  C  =  Na2CO3  +  Na2O  +  2H2. 

Theoretically,  to  produce  1000  cubic  feet  of  hydro- 
gen at  30  inches  barometric  pressure  and  40°  F.  by  this 
process,  222  Ib.  of  caustic  soda  and  16*61  Ib.  of  carbon 
are  required,  or  a  total  weight  of  pure  reagents  equal  to 
238*61  per  1000  cubic  feet  of  hydrogen  produced. 

The  hydrogen  produced  by  this  process  would  be 
liable  to  contain  traces  of  methane,  arsine,  and  sulphu- 
retted hydrogen,  the  amount  depending  on  the  purity  of 
the  coal  used. 

A  modification  of  this  process,  whereby  the  caustic 
soda  is  replaced  by  slaked  lime,  is  covered  by  a  patent 
taken  out  in  U.S.A.  by  Bailey  in  1887. 

With  a  Formate  or  Oxalate* — If  sodium  formate  is 


CHEMICAL    METHODS  61 

heated  with  caustic  soda  in  the  form  of  soda  lime,  the 
following  reaction  takes  place  :— 

H  .  COONa  +  NaOH  =  Na2CO3  +  H2. 

This  method  has  been  used  for  the  production  of 
hydrogen  in  the  laboratory  ;  however,  it  cannot  be  re- 
garded as  singularly  convenient. 

If  the  sodium  formate  is  replaced  by  sodium  or 
potassium  oxalate  a  similar  reaction  takes  place  : — 

Na2C2O4  +  2NaOH  =  2Na2CO3  +  H2. 

This  last  method,  it  is  interesting  to  note,  was  em- 
ployed by  Amagat  for  the  preparation  of  the  hydrogen 
for  his  classic  experiments  on  the  relationship  of  pressure 
to  volume. 

(3)  Methods  in  which  Hydrogen  is  Derived  from 

Water. 

Hydrogen  can  be  derived  from  water  by  means  of 
the  alkali  and  alkali  earths  groups  of  metals,  but  since 
all  these  are  expensive,  the  production  of  hydrogen  from 
these  sources  is  limited  to  the  requirements  of  the 
chemical  laboratory. 

With  Lithium. — If  metallic  lithium  is  placed  in 
water  it  is  attacked  by  it,  in  accordance  with  the 
following  equation,  with  the  production  of  hydrogen 
and  lithium  hydrate  : — 

2Li  +  2H2O  =  2LiOH  +  H2. 

It  is  interesting  to  note  that  since  metallic  lithium 
has  a  density  of  -59  (the  smallest  density  of  any  solid), 
it  floats  on  the  surface  of  the  water  while  it  is  being 
attacked. 


62  MANUFACTURE  OF  HYDROGEN 

With  Sodium, — If  metallic  sodium  is  placed  in 
water  it  is  attacked  by  it,  in  accordance  with  the  follow- 
ing equation,  with  the  production  of  hydrogen  and 
sodium  hydrate  : — 

2Na  +  2H2O  =  2NaOH  +  H2. 

Since  considerable  quantities  of  heat  are  given  out 
when  the  sodium  is  attacked  by  the  water,  much  of 
which  heat  is  communicated  to  the  metal,  it  frequently 
melts  while  being  attacked,  the  melting  point  of  the 
metal  being  95 '6°  C. 

While  the  above  equation  expresses  the  principal 
reaction  which  takes  place,  a  second  reaction  also 
occurs,  leading  to  the  production  of  sodium  hydride, 
which  is  somewhat  unstable  under  these  conditions  and 
occasionally  explodes  with  violence,  to  avoid  which  a 
piece  of  apparatus  has  been  designed  by  J.  Rosenfeld.1 

With  Potassium, —  If  metallic  potassium  is  placed  in 
water  it  is  attacked,  in  accordance  with  the  following 
equation,  with  the  production  of  hydrogen  and  potassium 
hydrate  :— 

2K  +  2H2O  =  2KOH  +  H2. 

Such  is  the  heat  which  is  liberated  during  the  re- 
action that  if  a  piece  of  potassium  is  placed  in  a  bucket 
of  water,  the  metal  is  carried  to  the  surface  by  the 
vigorous  stream  of  hydrogen  produced,  and  there  be- 
comes so  hot  as  to  ignite  the  hydrogen  evolved. 

The  same  remarks  which  have  been  made  as  to  a 
secondary  reaction  with  regard  to  sodium,  apply  with 
like  force  to  potassium. 

1  "  Prakt.  Chem.,"  48,  599-601. 


CHEMICAL    METHODS  63 

With  the  Alkaline  Earths. 

With  Magnesium.  —  If  metallic  magnesium  is  placed 
in  water  which  is  heated  to  its  boiling  point,  hydrogen  is 
slowly  evolved,  in  accordance  with  the  following  equa- 
tion, producing  hydrogen  and  magnesium  hydrate  :  — 
Mg  +  2H20  =  Mg(OH)2  +  H2. 

To  accelerate  the  reaction,  the  magnesium    is   gently 
heated  in  a  tube  and  steam  passed  over  it. 

With  Calcium.  —  If  metallic   calcium    is   placed  in 
water  at  ordinary  atmospheric  temperature  it  decomposes 
it  in  accordance  with  the  following  equation,  producing 
a  vigorous  stream  of  hydrogen  and  calcium  hydrate  :— 
Ca  +  2H2O  =  CatOH),  +  H,. 


With  Strontium.  —  A  similar  reaction  to  that  already 
given  for  calcium  takes  place,  but  somewhat  more  vigor- 
ously. 

With  Barium.  —  A  similar  reaction  to  that  already 
given  for  calcium  takes  place,  but  much  more  vigorously. 

THE  BERGIUS  PROCESS. 

With  Iron.  —  If  metallic  iron  is  heated  in  the  pres- 
ence of  water  under  very  high  pressure,  hydrogen  is 
evolved  and  magnetic  oxide  formed,  in  accordance  with 
the  following  equation  :— 

3Fe  +  4H2O  =  Fe3O4  +  4H2. 

This  method,  which  is  known  as  the  Bergius  process, 
was  put  into  commercial  operation  in  1913  at  Hanover. 
It  has  two  great  advantages  —  a  very  pure  hydrogen  is 
produced,  and  since  it  is  under  great  pressure,  it  can  be 


64 


MANUFACTURE  OF   HYDROGEN 


used  to  fill  bottles  without  the  use  of  a  compressor.  The 
chemical  composition  of  the  hydrogen  produced  is  given 
as  follows  : — 


Hydrogen 
Carbon  monoxide  . 
Saturated  hydrocarbons . 
Unsaturated  hydrocarbons 


99*95    Per  cent 
•ooi     „       „ 
•042     ,,       „ 
•008 


but  amount  of  the  carbon  compounds  must  be  greatly 
influenced  by  purity  of  the  iron  employed  ;  however, 
it  appears  to  be  a  fact  that  little  or  no  sulphuretted 
hydrogen  is  produced  even  if  the  iron  contains  appreci- 
able quantities  of  sulphur. 

While  it  has  been  stated  that  the  hydrogen  is  pro- 
duced by  the  action  of  water  at  high  temperature  and 
pressure  upon  metallic  iron,  this  does  not  entirely  de- 
scribe the  chemistry  of  the  process,  for  the  inventor  has 
found  that  the  presence  of  certain  metallic  salts  in  the 
solution,  and  also  other  metals,  greatly  increase  the 
speed  of  production  of  hydrogen.  The  following  com- 
parative table  of  productions  of  hydrogen  from  equal 
weights  of  iron  clearly  illustrates  this  point : — 


Temperature 

Volume  of  Hydrogen 
per  Hour. 

Iron  and  pure  water  . 

300 

230  c.c. 

Iron,  water,  and  ferrous  chloride 

300 

1390     ii 

Iron,  water,  ferrous  chloride,  and 

metallic  copper 

300 

193°     » 

Iron,  water,  ferrous  chloride,  and 

metallic  copper 

34° 

345°     n 

In  the  commercial  employment  of  this  process  it  is 
believed  that  the  working  pressure  is  about  3000  Ib. 
per  sq.  inch  and  the  temperature  350°  C. 


CHEMICAL    METHODS  65 

In  the  discharge  from  the  vessel  in  which  the  hydro- 
gen is  produced  there  is  a  reflux  condenser  which  effec- 
tively prevents  any  steam  from  escaping  from  the  plant 
when  the  hydrogen  is  drawn  off. 

One  of  the  remarkable  features  of  this  process  is  the 
fact  that  since  the  water  pressure  is  so  high,  it  penetrates 
right  into  the  iron  particles  ;  consequently  they  are  en- 
tirely employed,  and  a  yield  closely  approaching  the 
theoretical  is  obtained. 

Theoretically,  1000  cubic  feet  of  hydrogen  (at  30 
inches  barometer  and  40°  F.)  would  be  produced  with 
an  expenditure  of  1 16*5  Ib.  of  metallic  iron. 

The  size  of  the  plant  is  very  small  for  the  yields 
obtained,  it  being  stated  that  a  generator  of  10  gallons' 
capacity  gives  1000  cubic  feet  of  hydrogen  at  atmos- 
pheric temperature  and  pressure  per  hour. 

After  the  completion  of  the  reaction  the  pressure  can 
be  let  off  from  the  generator  and  the  magnetic  oxide  of 
iron  produced  removed  and  reduced  by  water  gas  to 
the  metallic  state,  when  it  can  again  be  employed  in  the 
process. 

It  is  claimed  that  the  cost  of  hydrogen  by  this 
process  is  exceedingly  low  ;  consequently,  if  this  is  cor- 
rect and  the  mechanical  difficulties  of  manufacturing 
generators  to  withstand  the  very  high  pressures  and 
chemical  action  are  satisfactorily  overcome,  this  process 
would  appear  to  be  one  of  the  highest  value  for  the  com- 
merciar  production  of  hydrogen. 

A  certain  amount  of  information  with  regard  to  this 
process  can  be  found  in  the  following  paper  :  "  Produc- 
tion of  Hydrogen  from  Water  and  Coal  from  Cellulose 
at  High  Temperatures  and  Pressures,"  by  F.  Bergius, 

5 


66  MANUFACTURE   OF   HYDROGEN 

the  "  Journal  of  the  Society  of  Chemical  Industry,"  vol. 
xxxii.,  1913. 

The  process  is  protected  by  the  following  patents  : — 

German  Patent,  254593,  1911. 

French  Patent,  447080,  1912. 

English  Patents,  19002  and  19003,  1912. 

United  States  Patents,  1059817,  1059818,  1913, 
all  in  the  name  of  F.  Bergius. 

While  the  previous  method  is  of  commercial  impor- 
tance, the  following  method  is  of  interest : — 

When  the  ordinary  process  of  rusting  of  iron  takes 
place,  hydrogen  is  evolved. 

It  is  generally  considered  that  iron  does  not  rust 
when  it  is  in  contact  with  perfectly  pure  water,  free 
from  carbon  dioxide  or  any  other  mild  acid.  In  the 
following  method  iron  filings  are  placed  in  a  steel  bottle 
partly  filled  with  water  saturated  with  carbon  dioxide ; 
the  bottle  is  then  closed  and  sealed.  It  is  then  agitated, 
the  following  reaction  taking  place  :— 

Fe  +  H20  +  C02  =  FeC03  +  Ha. 

This  method  is  one  of  interest  and  is  described  by 
Bruno  in  the  "  Bull.  Soc.  Chim.,"  1907,  [iv.],  1661.  It 
cannot,  however,  be  regarded  as  having  a  commercial 
use. 

With  Hydrides* — As  has  already  been  stated,  the 
hydrides  of  the  metals  of  the  alkali  and  alkaline  earth 
groups  produce  hydrogen  on  being  placed  in  water. 
However,  in  only  two  cases  are  these  reactions  worth 
consideration. 

With  Lithium  Hydride*— If  lithium  hydride  is 
brought  into  contact  with  water,  hydrogen  is  evolved 


CHEMICAL    METHODS  67 

and  lithium  hydrate  formed,  in  accordance  with  the  fol- 
lowing equation  : — 

Li4H2  +  4H2O  =  4LiOH  +  3H2. 

Such  is  the  rarity  of  lithium  at  the  present  time  that 
the  above  is  neither  a  commercial  nor  a  laboratory  method 
of  producing  hydrogen.  It  is,  however,  of  the  greatest 
interest,  owing  to  the  large  yield  of  hydrogen  obtained 
from  a  small  weight  of  lithium  hydride.  Theoretically, 
1000  cubic  feet  of  hydrogen  at  30.  inches  barometer 
and  40°  F.  are  produced  from  2776  Ib.  of  pure  lithium 
hydride  and  66 '6  Ib.  of  water.  Many  ingenious  ideas 
have  been  put  forward  for  the  employment  of  lithium 
hydride  in  airships  so  that  in  the  event  of  an  airship 
loosing  gas  from  some  cause,  this  may  be  replaced  by 
hydrogen  manufactured  in  the  airship.  As  has  been  seen, 
theoretically,  94*36  Ib.  of  reagents  are  required  to  pro- 
duce 1000  cubic  feet  of  hydrogen  at  30  inches  barometer 
and  40°  F.  Now  this  amount  of  hydrogen  would  have 
a  lift  of  74*06  Ib.,  so  if  the  products  of  the  manufacture 
of  hydrogen  were  dropped  the  buoyancy  of  the  ship 
would  be  increased  by  94*36  +  74'o6  Ib.,  or  168*42  Ib. 
for  every  94*36  Ib.  of  material  dropped  from  the  ship. 
However,  interesting  as  these  suggestions  are,  such 
is  the  rarity  and  cost  of  lithium  that  at  the  present 
time  they  are  not  capable  of  realisation,  though  future 
discoveries  of  lithium  minerals  and  cheaper  methods  for 
the  production  of  lithium  hydride  may  possibly  render 
these  ideas  of  practical  value. 

THE  HYDROLITH  PROCESS. 

With  Calcium  Hydride. — If  calcium  hydride  is 
brought  into  contact  with  water,  hydrogen  is  evolved 


68  MANUFACTURE  OF  HYDROGEN 

and  calcium  hydrate  formed,  in  accordance  with  the 
following  equation  : — 

CaH2  +  2H2O  =  Ca(OH)2  +  2H2. 

Theoretically,  to  produce  1000  cubic  feet  of  hydrogen 
at  30  inches  barometric  pressure  and  40°  F.,  58*4  Ib.  of 
pure  calcium  hydride  and  49*95  Ib.  of  water  are  required, 
or  a  total  weight  of  108*4  Ib.  of  pure  reagents  per  1000 
cubic  feet  of  hydrogen.  Since,  however,  water  does  not 
have  to  be  carried  in  most  parts  of  Europe,  the  theo- 
retical weight  to  be  carried  per  1000  cubic  feet  of 
hydrogen  required  is  58*4  Ib.  This  method,  known  as 
the  Hydrolith  process,  has  been  satisfactorily  employed 
by  the  French  Army  in  the  field  for  the  inflation  of 
observation  balloons,  the  calcium  hydride  being  packed 
in  air-  and  water-tight  boxes  for  transportation.  In  the 
commercial  production  of  calcium  hydride  small  quan- 
tities of  calcium  nitride  are  produced,  which,  when  the 
hydride  is  attacked  with  water  gives  rise  to  ammonia, 
in  accordance  with  the  following  equation  :— 
Ca3N2  +  6H2O  =  3Ca(OH)2  +  2NH3. 

However,  as  ammonia  is  very  readily  soluble  in 
water,  if  the  hydrogen  produced  in  the  process  is 
scrubbed  with  water  the  ammonia  is  almost  entirely  re- 
moved and  an  exceedingly  pure  hydrogen  results. 

This  process  is  protected  by  a  French  patent,  No. 
327878,  1902,  in  the  name  of  Jaubert. 

With  Metallic  Sodium  and  Aluminium  Silicide.— 

If  a  mixture  of  metallic  sodium  and  aluminium  silicide 
is  placed  in  water,  hydrogen  is  evolved,  with  the  pro- 
duction of  sodium  silicate  and  aluminium  hydrate,  in 
accordance  with  the  following  equation  : — 

Al2Si4  +  8Na  +  i8H2O  =  Al2(OH)fi  +  4Na2SiO3 


CHEMICAL    METHODS  69 

Theoretically,  1000  cubic  feet  of  hydrogen  at  30 
inches  barometer  and  40°  F.  are  produced  from  64*8  Ib. 
of  this  mixture.  It  is,  however,  believed  that  the 
practical  yield  is  about  80  per  cent,  of  this  figure. 

This  process  is  essentially  one  for  the  production  of 
hydrogen  for  war  purposes,  though  the  author  does  not 
know  of  any  actual  use  of  it.  The  mixture  can  be  made 
into  briquettes,  which  must  be  packed  into  air-  and  water- 
tight boxes.  The  method,  which  is  sometimes  known 
as  the  "  Sical  process,"  is  protected  by  a  United  States 
patent — 977442,  1910 — in  the  name  of  Foersterling  and 
Philipps. 

With  Aluminium. — If  ordinary  metallic  aluminium 
is  placed  in  even  boiling  water,  little  or  no  chemical 
action  takes  place.  However,  if  the  aluminium  is  first 
amalgamated  with  mercury  it  is  rapidly  attacked  by  hot 
water,  with  the  formation  of  aluminium  hydrate  and 
hydrogen,  in  accordance  with  the  following  equation  :— 

2A1  +  6H2O  =  A12(OH)6  +  3H2. 

Theoretically,  to  produce  1000  cubic  feet  of  hydro- 
gen at  30  inches  barometric  pressure  and  40°  F.,  50  Ib. 
of  aluminium  are  required. 

In  the  commercial  application  of  this  method  it  is 
not  necessary  to  amalgamate  the  metallic  aluminium 
with  mercury  by  hand,  as  advantage  is  taken  of  the 
fact  that  aluminium  will  reduce  aqueous  solutions  of 
salts  of  mercury  to  the  metallic  state,  in  accordance  with 
the  following  equation  :— 

2A1  +  3HgCl2  =  2A1CI3  +  3Hg. 

Consequently,  if  there  is  an  excess  of  aluminium  over 
that    required    by    the   equation,    this    excess    will    be 


70  MANUFACTURE  OF  HYDROGEN 

automatically  amalgamated  by  the  metallic  mercury  as 
it  is  produced. 

In  a  practical  application  of  this  method  by 
Mauricheau  Baupre,1  fine  aluminium  filings  are  mixed 
with  a  small  proportion  of  mercuric  chloride  (HgCl2) 
and  potassium  cyanide  (KCN),  which  causes  a  slight 
rise  in  temperature  and  produces  a  coarse  powder,  which 
is  quite  stable  if  kept  free  from  moisture.  This  mixture 
can  be  kept  in  air-  and  water-tight  boxes  until  it  is  re- 
quired, when  it  can  be  gradually  added  to  water  kept  at 
about  70°  C.  A  brisk  evolution  of  hydrogen  then  takes 
place  which  closely  approximates  to  the  theoretical  yield. 

Another  very  interesting  application  of  this  increased 
chemical  activity  of  aluminium  when  amalgamated  with 
mercury  is  incorporated  in  a  toy  which  is  sometimes 
seen  on  sale  under  the  name  of  "  Daddy  Tin  Whiskers  ". 
This  toy  consists  of  an  aluminium  stamping  of  a  face 
and  a  pencil,  the  core  of  which  is  filled  with  a  preparation 
chiefly  composed  of  a  mercury  salt.  It  is  operated  by 
rubbing  the  eyebrows  and  chin  with  this  special  pencil. 
Shortly  afterwards  white  hairs  of  aluminium  oxide 
(A12O3)  gather  wherever  the  pencil  has  touched  the 
aluminium. 

To  operate  the  above  process  for  the  manufacture 
of  hydrogen  it  is  necessary  that  the  aluminium  should 
be  as  pure  as  possible  and  should  not  contain  copper. 
The  commercial  light  alloy  known  as  "duralumin," 
which  contains  about  94  per  cent,  of  aluminium  and  4 
per  cent,  of  copper,  is  entirely  unsuitable  for  generating 
hydrogen  in  the  method  above  described,  as  it  is  almost 
unattacked  by  even  boiling  water  containing  a  small 
quantity  of  a  mercury  salt. 

luComptes  Rend.,"  1908,  147,  310-1. 


CHEMICAL    METHODS  71 

The  following  patents  deal  with  this  process  : — 

French  patent  392725,  1908,  in  the  name  of  Mauri- 
cheau  Baupre. 

English  patent  3188,  1909,  in  the  name  of  Gries- 
heim. 

German  patent  229162,  1909,  in  the  name  of  Gries- 
heim. 

With  Aluminium  Alloy. — The  following  alloy- 
Aluminium       .  ,        .        .        .78-98  parts. 
Zinc          .         .......     15-1  -5     „ 

Tin  .       7-0-5     „ 

is  made  and  cast  into  a  plate  ;  after  cooling  it  is  amalga- 
mated with  mercury.  After  amalgamation  the  plate  is 
heated  as  strongly  as  possible  without  volatilising  the 
mercury.  When  it  has  become  thoroughly  amalgamated 
it  is  allowed  to  cool  and  is  then  ready  for  use. 

If  this  alloy  is  put  into  hot  water  it  readily  yields 
hydrogen  ;  the  hydrogen  yield  is  proportionate  to  the 
aluminium  and  zinc  content. 

The  gas  produced  is  very  pure. 

This  process  is  protected  by  the  following  patent : 
Uyeno,  British  patent,  11838,  1912. 

With  Steam. 

In  considering  the  production  of  hydrogen  from 
steam,  a  considerable  number  of  processes  must  be  con- 
sidered in  which  the  first  stage  (which  is  common  to 
all  the  processes)  consists  in  the  manufacture  of  blue 
water  gas  ;  consequently,  prior  to  the  description  of 
these  processes,  amongst  the  most  important  of  which 
are  : — 


MANUFACTURE  OF  HYDROGEN 


The  Iron  Contact  process, 

The  Badische  process, 
The  Linde-Frank-Caro  process, 
the  manufacture  of  water  gas  will  be  described. 

THE  MANUFACTURE  OF  WATER  GAS. 

When  steam  is  passed  over  red-hot  carbon,  the  two 
following  chemical  reactions  take  place  :-— 

(1)  C  +  H2O  =  CO  +  H2. 

(2)  C  +  2H20  =  C02  +  2H2. 

The  question  as  to  which  equation  represents  the 
predominant  reaction  taking  place,  depends  on  the 
temperature  of  the  carbon  ;  roughly  speaking,  the  higher 
the  temperature  the  more  closely  does  the  reaction 
coincide  with  the  first  chemical  equation. 

The  following  experimental  results  (H.  Bunte,  "J.  fur 
Gasbeleuchtung,"  vol.  37,  81)  clearly  illustrate  the  effect 
of  temperature  on  the  chemical  composition  of  the  pro- 
ducts of  the  reaction  : — 


Composition,  by  Volume  of  Gas 

Temperature 

Per  Cent,  of  Steam 

Produced. 

°C. 

Decomposed. 

H2. 

CO. 

C02. 

674 

8-8 

65-2 

4'9 

29-8 

758 

25-3 

65-2 

7-8 

27-0 

838 

41-0 

6  1  '9 

15-1 

22'9 

954 

70-2 

53*3 

39*3 

6-8 

IOIO 

94-0 

48-8 

49'7 

i'5 

1125 

99'4 

5°'9 

48-5 

0-6 

In  the  first  of  the  chemical  equations  given,  it  will 
be  seen  that  the  products  are  composed  of  50  per  cent. 


CHEMICAL    iMETHODS  73 

hydrogen  and  50  per  cent,  carbon  monoxide,  while  in 
the  second,  the  composition  is  66*66  per  cent,  hydrogen 
and  3 3 '3 3  per  cent,  carbon  dioxide  ;  in  Dr.  Bunte's 
experiments,  figures  closely  approximating  to  the  first 
equation  were  obtained  when  the  temperature  of  the 
carbon  was  iooo°-iioo°  C,  while  figures  similar  to  the 
products  indicated  in  the  second  equation  were  found 
when  the  temperature  was  674°  C. 

Now,  whatever  purpose  water  gas  may  be  required 
for,  its  use  for  this  purpose  depends  on  the  fact  that  the 
gas  will  combine  with  oxygen  with  the  evolution  of 
heat,  consequently  the  plant  should  be  worked  to  make 
the  product  with  the  highest  calorific  power  for  the 
lowest  fuel  consumption.  This  requirement  is  reached 
more  closely  if  the  plant  is  operated  so  that  the  first 
equation  represents  the  chemical  reaction  which  takes 
place  ;  consequently,  in  the  practical  manufacture  of  water 
gas  the  coke  or  other  fuel  in  the  gas  producer  should 
be  at  a  temperature  of  about  1000°  C. 

The  chemical  reaction  producing  the  decomposi- 
tion of  the  steam  is  endothermic,  that  is  to  say,  as  the 
reaction  proceeds,  the  temperature  of  the  coke  falls,  so 
that  in  order  to  obtain  a  gas  approximating  to  the  pro- 
ducts in  the  first  equation,  heat  must  be  supplied  to  the 
coke,  to  counteract  the  fall  in  temperature,  due  to  its 
reaction  with  the  steam. 

In  the  oldest  type  of  plant,  the  coke  which  was  used 
for  the  manufacture  of  the  water  gas  was  in  a  cylinder, 
which  was  externally  heated  by  a  coke  or  coal  fire  ; 
however,  this  procedure  was  not  very  efficient,  and  the 
practice  is  not  in  use  at  all  at  the  present  time. 

In  practice  to-day  there  are  two  methods  of  making 
water  gas,  one  the  English  or  Humphrey  and  Glasgow 


;4  MANUFACTURE  OF   HYDROGEN 

method,  and  the  other  the  Swedish  or  Dellwick- 
Fleischer  method. 

English  Method* — It  has  already  been  pointed  out 
that  from  thermal  chemical  reasons,  the  coke  through 
which  the  steam  is  passing  in  the  manufacture  of  water 
gas  should  be  at  about  1000°  C.  in  order  to  obtain  good 
results,  and  that  as  a  result  of  the  reaction  between  the 
coke  and  steam,  the  temperature  of  the  former  falls, 
necessitating  the  addition  of  heat  to  the  coke  mass,  in 
order  to  keep  up  the  efficiency  of  the  process. 

It  is  in  the  method  of  maintaining  the  coke  tempera- 
ture that  the  English  and  Swedish  systems  differ.  In 
both  systems  the  coke  is  kept  at  the  proper  temperature 
by  shutting  off  the  steam  supply  from  time  to  time,  and 
blowing  air  through  the  coke,  the  products  of  the  air 
blast  passing  out  of  the  generator  through  a  different 
passage  to  those  of  the  steam  blast. 

The  effect  of  blowing  air  through  the  coke  is  of 
course  to  produce  heat,  for  the  following  reactions  to 
a  lesser  or  greater  extent  take  place  : — 

(1)  C  +  02  =  C02, 

(2)  CO2  +  C  =  2CO, 

and  the  heat,  which  is  produced  by  the  combustion  of 
some  of  the  coke,  heats  the  remainder,  thus  raising  its 
temperature,  so  that  the  air  blast  can  be  shut  off,  and 
the  steam  blast  again  turned  on. 

In  the  English  system  the  depth  of  the  coke  in  the 
generator  is  considerable,  consequently  the  carbon  di- 
oxide formed  at  the  base  of  the  fire  tends  to  be  reduced 
in  the  upper  part  of  the  fire  by  the  hot  coke,  in  accord- 
ance with  equation  (2),  therefore  in  the  English  system 
during  the  air  blast  a  combustible  gas  is  produced. 


CHEMICAL    METHODS  75 

However,  while  at  first  sight  this  might  appear  to  be  an 
advantage,  there  are  several  disadvantages  associated 
with  this  method  of  working.  In  the  first  place,  the 
gas  which  is  produced  during  the  air  blast,  though  com- 
bustible, is  not  a  gas  of  high  calorific  power,  as  it  contains 
such  a  large  amount  of  atmospheric  nitrogen  ;  in  fact, 
under  the  most  favourable  circumstances,  the  gas  pro- 
duced during  the  air  blast  will  not  contain  over  30  per 
cent,  of  carbon  monoxide,  while  the  rest  of  it  will  be  in- 
combustible, being  chiefly  nitrogen  together  with  some 
carbon  dioxide.  Another  disadvantage  of  this  system 
is  that  since  the  coke  is  permanently  burnt  only  to 
carbon  monoxide,  the  amount  of  heat  actually  generated 
in  the  coke  mass  is  comparatively  small,  consequently 
the  rate  of  temperature  rise  in  the  coke  mass  is  slow. 

In  the  Swedish  or  Dellwick-Fleischer  method,  the 
coke  temperature  is  from  time  to  time  raised  by  means 
of  an  air  blast,  but  in  this  case  the  depth  of  fuel  is 
relatively  shallow,  so  that  the  carbon  burnt  remains 
permanently  in  the  form  of  carbon  dioxide  ;  and  since  in 
burning  equal  weights  of  carbon  to  carbon  monoxide 
and  carbon  dioxide  over  three  times  as  much  heat  is 
generated  in  situ  when  the  carbon  is  burnt  to  carbon 
dioxide  than  when  burnt  to  carbon  monoxide,  the  rate 
of  rise  of  temperature  of  the  coke  mass  in  the  generator 
is  much  more  rapid  than  is  the  case  in  the  English 
system,  and  consequently  the  period  occupied  by  the 
air  blast  is  very  much  reduced. 

Fig.  6  shows  a  diagram  from  Dellwick's  English 
patent  29863,  1896,  illustrating  his  plant  for  the  produc- 
tion of  blue  water  gas. 

A  is  the  generator  provided  with  a  coke  receptacle 
B,  which  passes  through  a  stuffing-box  D  placed  on 


76  MANUFACTURE  OF   HYDROGEN 

the  cover  or  top  of  the  generator.  The  object  of  this 
receptacle  is  to  keep  the  fuel  height  constant  in  the 
generator  ;  if  B  is  kept  filled  with  fuel,  as  that  which 
is  on  the  grate  burns  away,  fresh  fuel  will  run  in  from  B 
and  will  keep  the  depth  of  fuel  on  the  grate  constant. 


FIG.  6. 

L  is  the  main  air  inlet,  while  a  secondary  supply 
of  air  takes  place  through  the  vertical  pipe  G,  the 
purpose  of  this  latter  air  inlet  being  to  ensure  a  thorough 
supply  of  air  to  all  parts  of  the  fuel  bed. 

S  and  S'  are  steam  inlets,  I  and  I'  are  gas  outlets, 
and  E  is  an  outlet  for  the  products  made  during  the  air 
blast. 


CHEMICAL    METHODS  77 

The  method  of  working  this  generator  would  be  as 
follows  : — 

When  a  coke  or  other  fire  of  suitable  depth  has  been 
obtained  on  the  grate,  the  receptacle  B  is  charged 
with  fuel,  and  the  lid  C  firmly  closed  ;  valves  I  and 
I'  are  closed  and  valve  F  opened,  then  air  under 
suitable  pressure  is  admitted  through  L  and  G  ;  this 
causes  the  fuel  to  burn  with  rise  in  temperature  of 
the  unburnt  portion,  while  the  products  of  combus- 
tion, containing  about  20  per  cent,  of  carbon  dioxide 
and  70  per  cent,  of  nitrogen,  escape  by  the  passage  E. 

When  the  temperature  of  the  coke  on  the  hearth  has 
been  raised  to  about  1000°  C.  the  air  blast  is  stopped, 
valve  F  closed,  valve  I'  opened,  and  steam  admitted 
through  S'  with  the  consequent  production  of  blue  gas, 
which  passes  out  to  a  scrubber  and  holder,  via  the 
valve  V. 

When  as  a  result  of  the  decomposition  of  the  steam 
by  the  fuel  mass,  the  temperature  of  the  latter  has  fallen 
below  the  economic  limit,  the  steam  supply  is  shut  off, 
and  the  air  blast  started  again  to  raise  the  fuel  tempera- 
ture. When  the  temperature  is  again  suitable,  the  air 
is  shut  off  and  steam  again  passed  through  the  fuel,  but 
on  this  occasion  downwards  from  the  steam  supply  S, 
the  water  gas  passing  out  by  the  outlet  I. 

The  object  of  this  alternation  of  the  direction  of  the 
steam  blast  is  to  keep  the  temperature  as  uniform  as 
possible  throughout  the  fuel  mass. 

Fig.  7  shows  a  modern  water  gas  producer,  which 
is  self-explanatory ;  the  fuel  charging  is  done  after 
every  third  steam  blast,  and  the  depth  of  the  fuel  kept 
correct  by  means  of  a  gauge  rod,  dropped  through  the 
lid  at  the  top  of  the  generator.  The  same  alternation 


MANUFACTURE  OF   HYDROGEN 


in  the  direction  of  the  steam  blast  is  maintained,  while 
during  the  air  blast  the  products  of  combustion  escape 
through  the  lid  at  the  top  of  the  generator,  which  is 
open  during  this  stage. 


V/!s/7  Outlet 


FIG.  7. 

The  sequence  of  operation  with  a  standard  gener- 
ator, having  a  circular  hearth  about  5  feet  6  inches  in 
diameter,  would  be  : — 


1 .  Air  blast 

2.  Steam  up 

3.  Air  blast 


2  minutes 
6       „ 
i  minute 


CHEMICAL   METHODS  79 

4.  Steam  down     .         .         .         .         .         .6  minutes 

5.  Air  blast          .         .         .         ...         .      i  minute 

6.  Steam  up         ......     6  minutes. 

At  the  end  of  the  last  operation,  additional  fuel  would 
be  added  and  the  sequence  again  started.  The  air 
supply  main  would  be  at  a  pressure  of  about  1 5  inches 
of  water  above  the  atmospheric,  while  the  steam  main 
would  be  at  about  1 20  Ib.  per  sq.  inch,  the  rate  of  flow 
of  the  steam  being  about  45  Ib.  per  minute,  during  the 
steaming  periods. 

Working  under  the  conditions  described,  using  coke 
of  the  following  composition  as  a  fuel : — 

Per  Cent. 
Moisture     .         .  .         .  6*0    by  weight. 

Ash   .......       9-0  „ 

Volatile  sulphur  .         .         .         .       1*35          „ 

Nitrogen    ......       0*6  ,, 

Carbon,  etc.  (by  difference)          .         .83-05          „ 


lOO'OO 

a  water  gas  of  about  the  following  composition  would 
be  obtained  : — 

Per  Cent. 

Hydrogen 52-0  by  volume. 

Carbon  monoxide          .         .         .         .39-6  „ 

Methane 0-4  „ 

Carbon  dioxide    .         .         .         .         •       3'5  ?> 

Sulphuretted  hydrogen          .         .         -0-5  „ 

Nitrogen .4-0  „ 

lOO'O 

for  a  consumption  in  the  generator  of  about  35-40  Ib.  of 
coke  per  1000  cubic  feet  of  blue  water  gas  measured  at 
atmospheric  temperature  and  pressure. 

A  consideration  of  this  coke  consumption  is  instruc- 


8o  MANUFACTURE   OF   HYDROGEN 

tive  ;  from  the  analysis  of  the  water  gas,  it  will  be  seen  in 
1000  cubic  feet  of  the  gas  there  are — 

396  cubic  feet  of  carbon  monoxide. 
35     ,,        »    »       »       dioxide. 

If  the  barometer  is  30  inches  and  the  temperature  60°  P\, 
1000  cubic  feet  of  carbon  monoxide  weighs  74*6  Ib. 

74-6  x  396 


•  '•  396  »» 


1000 

29-6  Ib. 


12 


But  carbon  monoxide  contains  —   of  its  total  weight  of  carbon. 

28 

29-6  x  12 
.•.  396  cubic  feet  of  carbon  monoxide  contains  ^ Ib. 

carbon  =  127  Ib. 
Similarly, 
1000  cubic  feet  of  carbon  dioxide  weighs  117-3  Ib. 

35  x   "7'3 


•*•  35 


IOOO 

-  4-1  Ib. 


But  carbon  dioxide  contains  --  of  its  total  weight  of  carbon. 

44 

/.  *z   cubic  feet  of  carbon  monoxide  contains  Ib.  of 

44 

carbon  =  i'i  Ib. 

Adding  these  two  results  together,  it  is  seen  that  while 
35-40  Ib.  of  coke,  equivalent  to  29-33  ^D-  °f  carbon,  are 
consumed  in  the  generator  per  1000  cubic  feet  of  water 
gas,  only  13*8  Ib.  of  this  carbon,  or  42-46  per  cent.,  are 
present  in  the  gas  produced,  the  bulk  of  the  remainder 
of  the  carbon  consumed  in  the  generator  being  burnt 
during  the  air  blast  period,  and  the  remainder  lost  in  the 
ash  pit,  and  during  clinkering ;  however,  while  these 
figures  are  instructive,  as  indicating  the  magnitude  of 
air  blast  consumption  of  fuel,  to  gain  comparative  figures 
it  is  necessary  to  obtain  the  calorific  power  of  the  coke 


CHEMICAL    METHODS  81 

consumed,  and  of  that  of  the  water  gas  produced  from 
a  given  weight  of  coke. 

If  35  Ib.  of  the  coke,  the  analysis  of  which  has  been 
already  given,  are  consumed,  in  the  production  of  1000 
cubic  feet  of  water  gas  at  30  inches  barometer  and  60° 
F.,  of  the  composition  which  has  also  been  given,  it  will 
be  found  that  the  calorific  power  of  the  coke  consumed, 
compared  with  that  of  the  gas  produced,  is  as 

516:342, 

that  is  to  say,  judged  on  a  thermal  efficiency  basis,  the 
efficiency  of  the  producer  working  under  these  condi- 
tions is 

34«  x   zoo  ,  66  t> 

5l6 

which  is  a  figure  such  as  is  obtained  in  ordinary  com- 
mercial water  gas  manufacture. 

The  analysis  of  the  water  gas  so  far  given  enumer- 
ates the  chief  constituents,  but  in  reality  there  are  traces 
of  other  products,  such  as  carbon  bisulphide,  car  bony  1 
sulphide,  and  thiophene,  derived  from  the  sulphur  in  the 
fuel,  which,  minute  in  quantity,  may  nevertheless  in  the 
certain  chemical  processes  produce  appreciable  and  un- 
desirable results  :  from  the  iron  contained  in  the  fuel, 
minute  amounts  of  iron  carbonyl  are  formed,  which  in 
most  processes  in  which  water  gas  is  used  is  a  matter 
of  no  importance,  but  if  the  gas  is  to  be  used  for 
lighting  with  incandescent  mantles,  its  removal  is  de- 
sirable. 

The  producer,  which  has  been  described,  is  not  in 
practice  absolutely  continuous  in  operation,  as  from 
time  to  time  the  process  has  to  be  interrupted  in  order 
to  remove  the  clinker  from  the  fire. 

6 


82  MANUFACTURE  OF  HYDROGEN 

The  process  of  "  clinkering,"  besides  requiring  labour, 
is  wasteful,  as  hot  fuel  as  well  as  clinker  is  drawn  from 
the  fire,  consequently  various  devices  have  been  designed 
to  make  self-clinkering  producers. 

The  majority  of  these  designs  consist  essentially 
of  a  rotating  conical  hearth.  Fig.  8  shows  a  device 
described  in  English  patent  246111,  1909,  which  is  al- 
most self-explanatory.  The  clinker  pan  h  and  the  blast 
nozzle  /  are  connected  and  free  to  rotate  on  the  ball  race 
shown  in  the  vertical  section.  The  end  of  the  blast 
nozzle  i  is  fitted  with  helical  excrescences  with  holes  k 
for  steam  and  air  in  their  trailing  edge.  During  the 
working  of  the  producer,  the  nozzle  and  clinker  pan  are 
rotated,  any  clinker  forming  being  broken  up  between 
the  helical  vanes  on  the  fixed  water  jacketed  body  of 
the  producer  and  those  on  the  rotating  blast  nozzle. 
The  clinker  on  being  broken  up  falls  into  the  clinker 
hearth,  which  is  filled  with  water  to  such  a  depth  as  to 
make  a  water  seal  between  the  producer  body  and  the 
moving  hearth. 

The  bottom  of  the  clinker  hearth  has  fixed  ribs, 
which  tend  to  hold  the  crushed  clinker,  which  during 
the  rotation  of  the  hearth  is  carried  round  until  it  is 
brought  against  the  fixed  vane  o  ;  this  lifts  it  out  of  the 
water. 

Producer  hearths  of  the  type  described  do  not  ap- 
pear to  effect  any  appreciable  saving  in  fuel,  but  since 
they  eliminate  clinkering,  they  have  a  decided  advantage, 
as  the  gas  yield  is  greater  in  a  given  time  than  would 
otherwise  be  the  case. 

Purification  of  Water  Gas, — For  most  industrial 
purposes,  it  is  necessary  that  the  crude  water  gas  should 


CHEMICAL   METHODS 


<1 


ft 


// 


7L 


Section  C.D. 
FIG.  8. 


84  MANUFACTURE  OF   HYDROGEN 

be  purified  before  its  ultimate  use.  For  practically 
every  process  in  which  water  gas  is  used  it  is  necessary 
that  it  should  be  freed  from  the  impurities  which  it 
mechanically  contains,  and  which  are  composed  of  ash 
and  dust,  carried  by  the  gas  from  the  producer. 

The  mechanically  retained  impurities  in  water  gas 
are  removed  by  scrubbing  the  gas  with  water,  that  is 
to  say,  by  passing  it  up  a  tower,  down  which  water  is 
falling.  Not  only  does  this  water  scrubbing  remove  the 
mechanically  retained  impurities,  but  it  also,  by  reducing 
the  temperature  of  the  gas,  causes  the  condensation  and 
removal  of  the  minute  quantity  of  iron  carbonyl  con- 
tained in  the  gas. 

Removal  of  Sulphuretted  Hydrogen. — For  most 
purposes  for  which  water  gas  is  required  it  is  desirable 
that  it  should  be  free  from  sulphuretted  hydrogen  ;  this 
is  usually  accomplished  by  passing  the  gas  at  about 
55°-65°  F.  over  hydrated  oxide  of  iron,  when  the  fol- 
lowing reaction  takes  place  :— 

Fe2(OH)8  +  3H2S  =  2FeS  +  6H2O  +  S. 

After  lapse  of  time,  the  hydrated  ferric  oxide  ceases  to 
have  any  sulphuretted  hydrogen-absorbing  power,  so 
the  gas  is  diverted  through  other  hydrated  oxide,  and 
the  spent  oxide  removed  and  placed  in  the  open  air, 
when,  after  moistening  with  water  and  exposure,  the 
following  reaction  takes  place  : — 

4FeS  +  6H2O  +  3O2  =  2Fe2(OH)6  +  48. 

Thus  it  is  seen  the  original  oxide  can  be  reproduced, 
and  on  reproduction  can  be  used  for  the  absorption  of 
fresh  sulphuretted  hydrogen.  In  practice  each  revivi- 
fication increases  the  free  sulphur  content  of  the  oxide 


CHEMICAL    METHODS  85 

about  7  per  cent,  and  as  time  goes  on  the  free  sulphur 
in  the  iron  oxide  increases  to  50-60  per  cent,  sulphur, 
when  it  commands  a  ready  sale  to  manufacturers  of  sul- 
phuric acid  ;  roughly  speaking,  i  ton  of  oxide  will  purify 
2,000,000  cubic  feet  of  gas  before  it  is  finally  spent. 

In  this  country,  it  is  not  generally  necessary  to  heat 
the  hydrated  oxide  of  iron  through  which  the  crude 
water  gas  is  passed,  as  the  heat  evolved  by  the  chemical 
reaction  is  sufficient  to  keep  the  oxide  at  a  suitable  tem- 
perature. However,  in  many  parts  of  the  world,  where 
the  winter  temperature  is  exceedingly  low,  it  is  neces- 
sary to  pass  steam  coils  through  the  oxide,  as  otherwise 
no  absorption  of  sulphuretted  hydrogen  takes  place. 

The  reason  for  this  failure  to  absorb  the  sulphuretted 
hydrogen  is  due  to  the  fact,  already  given  in  the  equa- 
tion, that  with  the  absorption  of  the  sulphuretted 
hydrogen,  water  is  produced,  which  freezes  on  the  sur- 
face of  the  hydrated  iron  oxide,  and  thus  prevents  further 
sulphuretted  hydrogen  coming  in  contact  with  it. 

In  the  practical  removal  of  sulphuretted  hydrogen, 
it  is  desirable  to  have  quite  a  considerable  amount  of 
water  in  the  hydrated  oxide  (about  15  per  cent,  by 
weight),  as  this  tends  to  keep  it  open  and  thus  keep  the 
pressure  necessary  to  get  the  water  gas  through  the 
oxide  quite  low  ;  it  is  also  desirable  to  keep  the  oxide 
alkaline,  consequently  about  i  per  cent,  of  lime  is  mixed 
with  it  to  accomplish  this. 

When  new  hydrated  oxide  is  put  in  water  gas 
purifiers,  even  though  it  may  contain  a  sufficiency  of 
water,  it  tends  to  cake  together  and  create  back 
pressure. 

This  can  be  prevented,  either  by  mixing  sawdust 
with  the  new  oxide  before  putting  it  in  the  purifiers 


86  MANUFACTURE  OF   HYDROGEN 

(about  i  part  to  5  of  oxide  by  volume)  or  by  mixing  some 
already  used  oxide  containing  a  considerable  amount  of 
free  sulphur  with  the  new  oxide  ;  this  also  tends  to  pre- 
vent caking. 

In  ordinary  commercial  purification  of  water  gas, 
100  tons  of  hydrated  ferric  oxide  will  effectively  purify 
200,000  cubic  feet  of  crude  water  gas  per  24  hours ; 
this  allows  of  keeping  20-30  tons  of  " revivified"  oxide 
in  reserve,  available  to  replace  the  working  oxide  as  it 
becomes  " spent". 

This  degree  of  purification  of  crude  water  gas  to  be 
used  in  the  manufacture  of  hydrogen  is  common  to  all 
the  processes  using  it ;  in  some  of  the  processes  special 
methods  of  purification  are  employed,  and  these  will  be 
given  in  the  description  of  the  process  which  renders 
such  methods  necessary. 

The  Iron  Contact  Process. 

Of  all  the  processes  for  the  production  of  hydrogen 
in  which  water  gas  represents  one  of  the  active  reagents, 
the  Iron  Contact  process  is  the  most  important,  as  it  is 
by  this  process  that  the  greater  amount  of  the  world 
production  of  hydrogen  for  use  in  industry  and  war  is 
at  present  made  ;  but  important  as  this  process  is,  it  is 
doubtful  if  it  will  maintain  its  present  pre-eminent  posi- 
tion during  the  next  few  years,  as  other  processes,  more 
economical,  but  at  present  not  so  reliable,  are  already  in 
existence,  and  with  lapse  of  time  greater  reliability  will 
probably  be  obtained  in  these  later  processes,  which  will 
result  in  the  Iron  Contact  process  occupying  a  less  im- 
portant position  in  hydrogen  production  than  it  does 
to-day. 

When   steam  is  passed  over    heated  metallic    iron, 


CHEMICAL    METHODS  87 

hydrogen  is  produced  in  accordance  with  the  following 
equation  :— 

3Fe  +  4H.p  =  Fe304  +  4H,. 

Theoretically,  to  produce  1000  cubic  feet  of  hydrogen 
at  30  inches  barometric  pressure  and  40°  F.,  116*5  lb. 
of  iron  and  49*95  Ib.  of  steam  are  required  :  however,  in 
practice  these  figures  are  not  closely  approached  because 
the  magnetic  oxide  of  iron  formed  tends  to  shield  the 
metallic  iron  from  the  action  of  the  steam  ;  indeed,  the 
reaction  may  be  regarded  as  merely  a  surface  one. 

When  the  protective  action  of  the  magnetic  oxide 
has  reached  such  a  degree  that  the  yield  of  hydrogen 
has  become  negligible,  the  supply  of  steam  is  stopped, 
and  the  water  gas  is  passed  over  the  magnetic  oxide, 
reducing  it  to  metallic  iron,  in  accordance  wkh  the  fol- 
lowing equations  :— 

Fe3O4  +  4H,  =  3Fe  +  4H2O 
t  Fe3O4  +  4CO  =  3Fe  +  4CO2. 

Then  further  steam  can  be  passed  over  the  iron,  with 
the  production  of  further  hydrogen. 

Thus,  it  is  seen  that  the  same  iron  is  used  continu- 
ously, and  steam  and  blue  water  gas  are  the  two  re- 
agents consumed.  Such  is  the  chemical  outline  of  the 
Iron  Contact  process  ;  however,  in  practice,  the  process 
is  somewhat  more  complex  and  very  much  less  efficient 
than  either  the  Electrolytic  process  or  the  Badische 
process,  both  of  which  are  described  at  a  later  stage,  nor 
can  the  hydrogen  produced  be  regarded  as  so  satisfactory 
for  some  industrial  purposes,  such  as  fat  hardening,  as 
that  made  by  the  other  two  processes. 

In  the  practical  working  of  the  Iron  Contact  process, 
the  process  is  not  begun  by  passing  steam  over  hot 


88  MANUFACTURE   OF   HYDROGEN 

metallic  iron,  but  by  manufacturing  the  iron  in  situ,  by 
reducing  iron  ore,  such  as  hematite,  with  the  water  gas, 
which  can  be  expressed  by  the  following  equations  :— 

2Fe2O3  +  3H2  =  2Fe  +  3H2O 
Fe2O3  +  sCO  =  2Fe 


The  advantage  of  this  procedure  is  that  a  spongy 
coating  of  metallic  iron  is  obtained  on  the  refractory 
iron  oxide,  with  the  result  that  the  iron  and  the  resulting 
magnetic  oxide  tend  to  be  held  together,  and  so  keep 
the  material  open,  and  therefore  free  from  back  pressure 
to  the  passage  of  the  steam  and  water  gas. 

In  practice,  to  obtain  a  yield  of  3500  cubic  feet  of 
hydrogen  per  hour,  about  6  tons  of  iron  ore  are  required. 
This  ore,  both  in  its  original  form  and  its  subsequently 
surface  altered  state,  is  kept  at  a  temperature  of  650°- 
900°  C.  ;  if  lower  than  650°  C.  the  reactions  become  very 
slow,  and  if  higher  than  900°  C.~  the  material  tends  to 
frit,  and  become  less  open,  thus  creating  resistance  to 
the  flow  of  gas  and  steam. 

In  the  practical  working  of  the  Iron  Contact  process, 
the  process  consists  of  three  stages  :— 

1.  Reducing. 

2.  Purging. 

3.  Oxidising. 

Reducing.  —  The  reducing  stage  consists  in  passing 
water  gas  over  the  heated  oxide,  thus  producing  a  coat- 
ing of  metallic  iron  on  the  oxide.  During  the  first 
moment  of  reducing  the  reaction  is  comparatively 
effective,  but  with  fewer  opportunities  for  the  gas  to 
come  into  contact  with  unacted-upon  oxide,  the  water 
gas  is  less  and  less  effectively  used,  and  consequently 
the  gas  on  leaving  the  retorts  contains  more  and  more 


CHEMICAL   METHODS 


89 


hydrogen  and  carbon  monoxide  as  the  reaction  con- 
tinues. 

This  variation  in  the  efficiency  of  reduction,  with 
lapse  of  time,  is  clearly  illustrated  in  the  graph,  Fig.  9, 
which  shows  the  carbon  monoxide  and  carbon  dioxide 
content  of  the  water  gas  after  passing  at  the  rate  of 
9000  cubic  feet  per  hour  over  4*2  tons  of  iron  oxide, 
heated  to  750°  C. 

In  practice,  it  is  found  that  the  speed  of  reduction  is 


bu 
55 

I45 
^40 

^35 
20 

i 

\, 

\ 

^"^ 

^. 

*-s   , 

"-^ 

^ 

» 

~—  ^, 

—  *^ 

--*. 

1  —  ^, 

,,- 

rr^ 

—  —  _  • 



e^- 

_--  • 

—  - 

^- 

^**' 

Weight  of  Ox 

ide.= 
ater 

=4-2  tons. 

- 

r-'" 

Volt 

me 

TfW 

3ae.= 

-900 

)cu.i 

•t.pe 

rhoi 

jr. 

01234567 


8      9     10     11     1Z     13    14    15     16     17     18 
Minutes. 


FlG.   9. 


much  slower  than  the  speed  of  oxidation,  consequently, 
in  practice,  the  duration  of  the  various  stages  is  ;— 

Reducing.  .  -.  .  .  20  minutes. 
Purging  .....  35  seconds. 
Oxidising  .....  9  minutes,  25  seconds. 

Purging.  —  When  the  reducing  stage  is  stopped,  the 
retort  or  retorts,  containing  the  surface  reduced  oxide, 
is,  or  are,  filled  with  an  atmosphere  of  partly  altered 
water  gas  ;  consequently  when  steam  is  turned  on 
hydrogen  is  produced  contaminated  with  the  residual 
water  gas  ;  thus  impure  hydrogen  is  allowed  to  flow 


90  MANUFACTURE  OF  HYDROGEN 

into  some  receptacle,  where  it  is  subsequently  used  for 
heating,  or  some  other  process,  which  will  be  described 
later. 

At  the  end  of  35  seconds  the  outflow  of  the  gas  is 
altered,  and  the  now  comparatively  pure  hydrogen  is 
directed  into  a  gas  holder,  or  wherever  it  may  be  re- 
quired. 

Oxidising. — The  oxidising  stage  is  exactly  the  same 
as  the  purging  stage,  except  as  to  the  direction  of  out- 
flow of  the  resulting  hydrogen. 

In  normal  working  the  gas  produced  has  approxi- 
mately the  following  composition  : — 

Per  Cent, 
by  Volume. 

Hydrogen 97-5 

Carbon  dioxide           .          .         ..          .          .          .  1-5 

„      monoxide      ......  -5 

Sulphuretted  hydrogen       .....  -03 

Nitrogen  (by  difference)      .          .          .          .         .  -47 


lOO'OO 


Purification  of  Crude  Hydrogen. — The  crude  hy- 
drogen is  first  scrubbed  with  water,  which  besides  re- 
moving mechanically  contained  impurities  also  reduces 
the  amount  of  carbon  dioxide,  as  this  gas  is  soluble  in 
water. 

The  hydrogen  is  then  passed  through  boxes  con- 
taining slaked  lime,  where  both  the  carbon  dioxide  and 
sulphuretted  hydrogen  are  absorbed  in  accordance  with 
the  following  equations  :— 

Ca(OH)2  +  C02  =  CaCO,  +  H2O, 

Ca(OH),  +  H2S  «  CaS  +  2H,O. 

However,  since  there  is  no  simple  process  of  revivi- 


CHEMICAL    METHODS  91 

Tying  the  lime  after  use,  it  is  probably  better  practice  to 
pass  the  crude  hydrogen  first  through  an  iron  oxide  box, 
identical  with  that  used  in  purifying  water  gas  ;  here  the 
sulphuretted  hydrogen  would  be  absorbed,  and  then  the 
gas  would  pass  on  to  a  lime  box,  where  the  carbon  di- 
oxide would  be  absorbed,  as  already  stated  ;  however, 
whichever  procedure  is  adopted  as  to  the  purification, 
a  gas  of  the  following  approximate  composition  is 
obtained : — 

Hydrogen  .         .         .         .         .         .         ...  99*0 

Carbon  dioxide    .         ......  nil 

„      monoxide -5 

Sulphuretted  hydrogen          *         .         .         .         .  trace 

Nitrogen  (by  difference)       .         .         .                  .  -5 


lOO'O 


Secondary  Chemical  Reactions, — The  fundamental 
chemical  reactions,  whereby  hydrogen  is  produced  by 
the  use  of  water  gas  and  steam  alternately,  in  the 
presence  of  iron  oxide,  have  now  been  given  in  con- 
siderable detail,  and  so  far  there  does  not  appear  any 
reason  why  the  same  iron  ore  should  not  be  used  in- 
definitely ;  however,  there  are  two  reasons  which  neces- 
sitate the  replacement  of  the  ore  from  time  to  time. 
The  first  reason  for  the  deterioration  of  the  ore  is  purely 
physical,  while  the  second  is  partly  chemical  and  partly 
physical  The  physical  reason  for  the  gradual  failure 
of  the  material  is  due  to  the  fact  that  with  constant  use 
the  ore  tends  to  break  up  into  smaller  and  smaller  pieces, 
thus  creating  back  pressure  to  the  flow  of  water  gas  and 
steam  ;  consequently  a  condition  arises  from  this  dis- 
integration of  the  ore  which  necessitates  its  replace- 
ment. 


92  MANUFACTURE  OF   HYDROGEN 

When  carbon  monoxide  is  in  contact  with  hot  metal- 
lic iron,  the  following  reaction  slowly  takes  place  :— 
Fe  +  6CO  =  FeC3  +  3CO2. 

Such  a  condition  arises  in  the  Iron  Contact  process 
towards  the  end  of  the  reducing  stage,  while  during  the 
oxidising  stage  the  following  reaction  slowly  takes 
place  : — 

3FeC:i  +  i3H2O  =  9CO  +  Fe3O4  +  isH,. 

Thus,  by  the  continued  operation  of  the  process,  there 
tends  to  be  an  increasing  amount  of  carbon  monoxide 
in  the  resulting  hydrogen.  There  are  two  methods 
whereby  this  difficulty  can  be  dealt  with  :  one  is  antici- 
patory, and  consists  in  adding  a  volume  of  steam l  to 
the  water  gas,  prior  to  its  passage  over  the  iron  oxide, 
equal  to  about  one-half  the  carbon  monoxide  content  of 
the  gas.  This,  while  slightly  retarding  the  speed  of 
reduction  of  the  oxide,  prevents  the  absorption  of  carbon 
by  the  metallic  iron,  formed  during  the  reduction,  and 
consequently  allows  of  hydrogen  of  high  purity  being 
produced.  The  other  method  is  intermittently  employed 
and  consists  in  occasionally  passing  air  over  the  carbon- 
contaminated  iron  oxide,  when  the  following  reaction 
takes  place  :— 

4FeC3  +  150^  =  2Fe2Oa  +  i2CO2, 

thus  allowing  after  reduction  a  purer  hydrogen  to  be 
made.  However,  this  process,  known  as  "  burning  off," 
while  undoubtedly  improving  the  purity  of  the  hydrogen 
subsequently  produced,  appears  to  hasten  the  disintegra- 
tion of  the  oxide,  contributing  to  the  necessity  for  its 
ultimate  replacement,  owing  to  the  high  back  pressure 
this  physical  condition  produces. 

1  French  patent  395132,  1908,  Dell  wick- Fleischer  Wassergas  Ges, 


CHEMICAL    METHODS  93 

The  minute  quantities  of  sulphuretted  hydrogen 
present  in  the  crude  hydrogen  arise  from  two  causes, 
the  first  of  which  is  sulphur  in  the  original  ore,  which, 
during  the  oxidising  stage,  produces  sulphuretted  hydro- 
gen, while  the  other  is  due  to  the  small  quantities  of 
sulphuretted  hydrogen  present  in  the  purified  water  gas, 
which  during  the  reducing  stage  are  absorbed  by  the 
iron  in  the  retorts  as  ferrous  sulphide,  which  is  subse- 
quently decomposed  during  the  oxidising  stage,  thus  :— 

FeS  +  H2O  =  FeO  +  H2S, 
3FeO  +  H2O  =  Fe3O4  +  H2. 

With  regard  to  the  sulphuretted  hydrogen,  which  is 
produced  merely  from  the  sulphur  originally  contained 
in  the  ore,  this  decreases  with  time;  ore  which  when 
put  in  the  retorts  contained  75  per  cent,  of  sulphur,  after 
a  year  in  continuous  use  contained  only  0*03  per  cent. 

Iron  Contact  Plant. — The  fundamental  and  second- 
ary chemical  reactions  involved  in  this  process  having 
been  considered,  there  remains  only  the  plant,  and  the 
actual  fuel  consumption  per  1000  cubic  feet  of  hydrogen 
to  be  described. 

The  Iron  Contact  plant  is  commercially  manufactured 
in  two  distinct  types  : — 

1.  The  Multi- Retort  type. 

2.  The  Single  Retort  type. 

Fig.  10  shows  a  purely  diagrammatic  arrange- 
ment of  a  multi-retort  generator.  The  retorts  are  ex- 
ternally heated  by  means  of  a  gas  producer  incorporated 
in  the  retort  bench.  The  even  heating  of  the  retorts  is 
secured  by  the  use  of  refractory  baffles  (not  shown)  and 
by  the  admission  of  air  for  the  proper  combustion  of  the 
producer  gas  at  different  points. 


94 


MANUFACTURE  OF   HYDROGEN 


The  retorts  are  arranged  so  that  either  blue  water 
gas  or  steam  can  be  passed  through  them  by  the  opera- 
tion of  the  valves  A  and  B. 

During  the  reducing  stage  the  valves  A  and  D  are 
open,  and  B  and  C  shut ;  thus  the  reducing  gas  passes 
through  the  oxide,  and  since  in  practice  the  whole  of  the 
carbon  monoxide  and  hydrogen  in  the  water  gas  is  not 
used  up  in  its  passage  through  the  retorts,  it  is  passed 

A  B 


FIG.   10. 

back  outside  of  them,  giving  up  its  remaining  heat,  and 
consequently  contributing  to  the  external  heating. 

On  the  reducing  stage  being  complete,  the  valves 
A  and  D  are  closed,  and  B  and  C  opened  ;  steam  passes 
through  the  retorts,  and  hydrogen  issues  past  the  valve 
C  to  the  water  seal,  and  thence  to  scrubbers  and  purifiers, 
and  finally  to  the  gasholder. 

When  high  purity  hydrogen  is  required,  on  the  re- 
ducing stage  being  complete,  the  valve  A  is  first  closed, 
and  then  the  valve  B  turned  on,  allowing  the  hydrogen 


CHEMICAL    METHODS 


95 


first  made  to  pass,  together  with  the  residual  gas,  in 
the  retorts  via  the  valve  D.  When  this  purging  has 
continued  for  about  half  a  minute,  C  is  opened  and  D 
closed,  the  hydrogen  produced  passing  via  the  water 
seal  ultimately  to  the  gasholder. 

Fig.    1 1  shows  a  diagram  of  a  single  retort  plant 


/J 


FIG. 


taken  from   Messerschmitt's  specification,  contained  in 
English  patent  No.  18942,  1913. 

This  plant  is  circular  in  plan,  and  consists  essentially 
of  two  cast-iron  cylinders  (19)  and  (20),  the  first  of 
which  is  supported  on  its  base  and  free  to  expand  up- 
wards, while  the  other  is  hung  from  a  flange  at  its  top, 
and  is  free  to  expand  downwards.  The  annular  space 


96  MANUFACTURE  OF   HYDROGEN 

(3)  between  the  two  cylinders  is  filled  with  suitable 
iron  ore,  while  the  circular  space  inside  the  smaller 
cylinder  (19)  is  filled  with  a  checker  work  of  refractory 
brick  (8).  The  plant  is  operated  by  first  heating  the 
refractory  bricks  (8)  by  means  of  water  gas  and  air, 
admitted  through  pipes  (15)  and  (16),  the  products  of 
combustion  going  out  to  a  chimney  by  the  pipe  (18). 
The  heating  of  the  checker  work  is  communicated  by 
conduction  to  the  ore  mass  (3) ;  when  this  is  at  a  suit- 
able temperature  (about  750°  C.)  the  gas  supply  (15)  is 
shut  and  water  gas  enters  by  the  pipe  (10),  passing 
up  through  the  ore  and  reducing  it  in  accordance  with 
the  equations  already  given.  When  the  reducing  gas 
reaches  the  top  of  the  annular  space  (3)  it  mixes  with 
air  entering  by  the  pipe  (16)  and  the  unoxidised  portion 
(the  amount  of  which  varies,  as  has  been  shown  in  the 
graph,  Fig.  9)  burns,  heating  up  the  brick  work, 
and  finally  passing  away  to  the  chimney  by  the  pipe 
(18). 

When  reduction  is  complete  (after  about  twenty 
minutes)  pipes  (16)  and  (10)  are  closed,  and  steam  is 
admitted  through  the  pipe  (17),  which  passes  upwards 
through  the  checker  work  (8)  becoming  superheated, 
and  then  down  through  the  contact  mass  (3),  where  it  is 
decomposed  in  accordance  with  the  equations  already 
given,  producing  hydrogen,  which  passes  out  by  the 
pipe  (12),  through  a  water  seal,  and  thence  to  a  gas- 
holder. Where  very  pure  hydrogen  is  required,  a 
purging  period  can  be  introduced  by  adopting  the 
following  procedure  : — 

When  reduction  is  complete,  pipes  (18)  and  (16)  are 
closed,  but  pipe  (10)  is  left  open,  and  (12)  still  remains 
closed. 


CHEMICAL    METHODS  97 

On  the  admission  of  steam  by  the  pipe  ( 1 7)  hydrogen 
is  generated  in  the  reaction  space  (3),  which,  together 
with  the  residual  water  gas,  is  forced  back  into  the 
water  gas  main  (10),  thus  tending  to  increase  the 
hydrogen  content  of  the  water  gas  in  the  gasholder. 

After  the  lapse  of  sufficient  time  (about  half  a 
minute)  pipe  (12)  is  opened  and  (10)  shut,  the  hydrogen 
subsequently  produced  passing  via  the  water  seal  to 
the  hydrogen  holder.  After  the  ore  has  originally  been 
heated  by  means  of  water  gas  and  air,  admitted  by 
pipes  (15)  and  (16),  the.  heat  can  be  maintained  entirely 
by  the  combustion  of  the  unoxidised  water  gas,  during 
the  reducing  stage,  by  the  admission  of  air  by  the  pipe 
(16) 

"  Burning  off"  can  be  accomplished  by  the  admis- 
sion of  air  by  the  pipe  ( 1 1 ),  the  products  passing  out  by 
the  pipe  (18).  The  top  of  the  plant  is  fitted  with  four 
weighted  valves,  one  of  which  is  shown  at  (14).  The 
Messerschmitt  plant  is  not  in  commercial  employment 
in  this  country,  but  it  is  considerably  used  both  in 
Germany  and  in  the  United  States,  where  the  standard 
unit  contains  about  5  tons  of  iron  ore,  with  a  production 
of  over  3000  cubic  feet  per  hour, 

Fuel  Consumption.— -In  the  multi-retort  type  of 
plant,  the  consumption  of  water  gas  is  about  2*5  cubic 
feet  per  cubic  foot  of  hydrogen  produced,  while  in  the 
single  retort  type,  where  the  water  gas  is  employed 
both  for  reduction  and  heating,  the  consumption  is 
about  3*5  per  cubic  foot  of  hydrogen  produced.  In 
each  type  of  plant,  if  the  same  kind  of  coke  is  used, 
both  for  the  production  of  water  gas  and  for  all  heating, 
including  steam  raising,  both  for  the  process  and  for  its 

7 


98  MANUFACTURE   OF   HYDROGEN 

auxiliary  machinery,  such  as  blowers,  feed  pumps,  etc., 
the  hydrogen  yield  from  each  is  about  : — 

6500-7000  cubic  feet  of  hydrogen  per  ton  of 
average  soft  coke. 

Relative  Advantages  of  the  Multi'  and  Single  Re- 
tort Plants. — While  in  fuel  consumption  there  is  little 
to  choose  between  the  two  plants,  there  is  undoubtedly 
less  complication  in  the  single  retort  plant  than  in  the 
multi,  owing  to  the  fewer  joints,  etc.,  which  are  at  high 
temperature. 

Another  advantage  in  the  single  retort  type  lies  in 
the  fact  that  fuel  is  consumed  at  two  points  only  : — 

1.  For  the  production  of  steam,  for  the  process  and 
auxiliary  machinery. 

2.  For  the  production  of  the  necessary  water  gas. 
In  the  multi-retort  type,  there  is  also  fuel  required 

for  the  supply  of  the  producer,  which  heats  the  retort 
bench ;  however,  this  additional  complication  can  be 
eliminated  by  heating  the  retorts  externally  by  means 
of  water  gas,  a  procedure  which  is  adopted  in  at  least 
one  commercial  hydrogen  plant. 

With  the  gradual  failure  of  the  retorts  themselves 
from  their  oxidation  by  the  steam,  the  advantage  again 
lies  with  the  single  retort  type,  as  it  is  a  simpler  job  to 
draw  the  cast-iron  liners,  and  replace  them,  than  it  is  to 
replace  the  individual  retorts  and  make  the  various  pipe 
joints. 

To  sum  up,  while  in  chemical  efficiency  there  is 
little  to  choose  between  the  two  types,  the  advantage  on 
the  whole  appears  to  lie  with  the  single  retort  type,  on 
account  of  its  greater  simplicity  of  repair. 

The  following  patents  with  regard  to  this  process  are 
in  existence  : — 


Oettli. 
Betou. 

Lewes.  ,, 

Hills  &  Lane. 
Elworthy.  U.S. 

Vignon.  French 

Lane  &  Monteux.       „ 
Dellwick  &  Fleis- 
cher. 
Lane. 


CHEMICAL    METHODS 


English  patent 


Caro. 

Strache. 

Messerschmitt. 


Lane. 


English 
German 

U.S.' 

English 

German 

U.S. 


Badische  Anilin 

und  Soda 

Fabrik.  French 

Messerschmitt. 


Badische  Anilin 

und  Soda 

Fabrik. 
Badische  Anilin 

und  Soda 

Fabrik. 


English 


French 


b 

99 

16759. 

1885. 

7518. 

1887. 

20752. 

1890. 

10356. 

1903. 

778182. 

1904. 

37327L 

1907. 

386991. 

1908. 

395132. 

1908. 

I759L 

1909. 

11878. 

1910. 

249269. 

1910. 

253705. 

1910. 

971206. 

1910. 

12117. 

1912. 

263390. 

1912. 

263391. 

1912. 

268062. 

1912. 

1028366. 

1912. 

1040218. 

1912. 

440780. 

1912. 

461480. 

1913. 

461623. 

I9I3- 

18942. 

453077. 
459918.      1913. 


TOO  MANUFACTURE   OF   HYDROGEN 

Lane.  U.S.  patent  1078686.  1913. 
Berlin  Anhaltische 

Maschinenbau.  English  ,,  28390.  1913. 

Pintoch.  French  ,,  466739.  1913. 
Berlin  Anhaltische 

Maschinenbau.   English       ,,  6155.  1914. 

With  Barium  Sulphide. —  In  the  previous  process 
which  was  considered,  steam  was  decomposed  by  means 
of  spongy  iron  ;  in  the  present  process,  instead  of  iron, 
barium  sulphide  is  used.  If  steam  is  passed  over  bar- 
ium sulphide  heated  to  a  bright  red  heat,  the  following 
reaction  takes  place  : — 

BaS  +  4H2O  =  BaSO4  +  4H2. 

The  barium  sulphate  produced  may  be  reduced  by 
heating  with  coke  to  barium  sulphide  in  accordance 
with  the  following  equation  : — 

BaSO4  +  C  =  BaS  +  4CO. 

The  barium  sulphide  can  be  employed  for  the 
generation  of  fresh  hydrogen  and  the  carbon  monoxide 
can  be  used  for  supplying  a  portion  of  the  heat  which  is 
required  for  the  process. 

The  process  is  protected  by  French  patent  361866, 
1905,  in  the  name  of  Lahousse. 

A  somewhat  similar  process  to  the  Lahousse  has 
been  protected  by  French  patent  447688,  1912,  in  the 
names  of  Teissier  and  Chaillaux.  In  this  process  bar- 
ium sulphate  is  heated  with  manganous  oxide,  when  the 
following  reaction  takes  place  :— 

BaSO4  +  4MnO  =  BaS  +  4MnO2. 
The  resulting  mixture  of  barium  sulphide  and  man- 


CHEMICAL; -METHODS-,  r.  :.  -  :  >„    lot 

ganese  dioxide  is  then  raised  to  a  white  heat,  when  the 
following  reaction  takes  place  : — 

BaS  +  4MnO2  =  BaS  +  4MnO  +  2O2. 

When  the  reaction  is  complete,  steam  underpressure 
is  passed  over  the  mixture  of  barium  sulphide  and  man- 
ganous  oxide,  with  the  production  of  hydrogen,  in  ac- 
cordance with  the  following  equation  :— 

BaS  +  MnO  +  4H2O  =  BaSO4  +  MnO  +  4H2. 

The  process  is  then  ready  to  be  started  again. 
Whether  it  will  have  a  considerable  commercial  applica- 
tion remains  yet  to  be  proved. 

THE  BADISCHE  CATALYTIC  PROCESS. 

Using  a  Catalytic  Agent. — In  the  processes  so  far 
described  for  the  production  of  hydrogen  from  steam, 
the  steam  has  been  decomposed  by  the  action  of  some 
solid  which  itself  undergoes  a  distinct  chemical  change 
requiring  treatment  to  bring  it  back  into  a  form  in  which 
it  can  be  again  used  for  the  production  of  hydrogen. 
In  the  process  about  to  be  described  the  steam  is  de- 
composed by  virtue  of  a  catalytic  agent  which  itself 
undergoes  no  permanent  change. 

This  process,  which  is  protected  by  patents  (enumer- 
ated at  the  end  of  this  note)  by  the  Badische  Anilin 
und  Soda  Fabrik  Gesellschaft,  consists  of  the  following 
stages  : — 

First,  Blue  Water  Gas  is  prepared  in  an  ordinary 
producer  and  purified  from  suspended  matter  by  means 
of  a  scrubber  ;  then  into  this  clean  water  gas  steam  is 
introduced  and  the  mixture  passed  over  a  catalytic 
material,  where  the  following  reaction  takes  place  :— 

Water  gas 

H2  +  CO  +  H2O  =  2H2  +  CO2. 


102     .   /.MANUEACTURE;OF   HYDROGEN 

Thus  it  is  seen  that  the  carbon  monoxide  contained 
in  the  blue  gas  is  oxidised  by  the  steam,  which  itself  is 
decomposed  with  the  production  of  hydrogen. 

Now  carbon  dioxide  is  readily  soluble  in  water, 
consequently  the  product  of  the  reaction  is  passed  under 
pressure  through  water,  where  it  is  absorbed,  leaving  a 
comparatively  pure  hydrogen. 

Starting  with  blue  water  gas,  which  may  be  roughly 
taken  as  being  composed  of  50  per  cent,  hydrogen  and 
50  per  cent,  carbon  monoxide,  the  composition  of  the 
gas,  after  the  introduction  of  the  steam  and  passage  over 
the  catalyst,  is  approximately  as  follows  :— 

Per  Cent, 
by  Volume. 
Hydrogen          .......         65 

Carbon  dioxide  .         .         .         .         .         .         30 

„       monoxide       ......     1*2-1 '8 

Nitrogen 2-5-4 

The  bulk  of  the  carbon  dioxide  is  absorbed  by 
means  of  water,  but  if  the  hydrogen  is  required  for 
aeronautical  purposes,  the  gas  is  finally  passed  through 
either  a  caustic  soda  solution  or  over  lime.  Traces  of 
carbon  monoxide  are  removed  by  passing  the  gas  under 
pressure  through  ammoniacal  cuprous  chloride  solution. 
As  a  result  of  these  final  purifications  a  gas  is  obtained 
of  approximately  the  following  composition  :  — 

Per  Cent, 
by  Volume. 

Hydrogen 97 

Nitrogen     .         .         .         .         .         .         .         .         27 

Carbon  dioxide    ....... 

„       monoxide -3 

In  practice  it  was  stated  that  in  commercial  iron- 
contact  plants  the  consumption  of  blue  gas  was  from 


CHEMICAL    METHODS  103 

2 '3  to  3 '5  cubic  feet  per  cubic  foot  of  hydrogen  ulti- 
mately produced. 

In  the  method  which  has  just  been  described  the 
consumption  of  blue  gas  is  about  i'i  to  1*3  cubic  feet 
per  cubic  foot  of  hydrogen,  or  assuming  a  consumption 
of  35  Ib.  of  coke  per  1000  cubic  feet  of  water  gas  pro- 
duced, the  hydrogen  yield  is  49,000  to  58,000  cubic  feet 
per  ton  of  soft  coke. 

In  the  operation  of  this  process,  the  blue  water  gas, 
together  with  a  requisite  amount  of  steam,  is  passed  over 
the  catalytic  material  at  a  temperature  of  400°  to  500°  C. 
Since  the  oxidation  of  the  carbon  monoxide  is  exother- 
mic, after  the  reaction  chamber  is  heated  to  the  tem- 
perature of  400°  to  500°  C.,  no  more  heat  need  be 
supplied  from  external  sources. 

The  chemical  composition  of  the  catalyst  appears  to 
be  somewhat  variable,  but,  as  in  the  case  of  the  catalyst 
used  in  the  fat-hardening  industry,  its  physical  condition 
effects  the  efficiency  of  the  process.  In  the  patents  pro- 
tecting this  process  a  variety  of  methods  are  described 
for  the  preparation  of  the  catalyst,  but  the  following 
may  be  given  as  representative  :— 

"  Dissolve  a  mixture  of  40  parts  by  weight  of  ferric 
nitrate,  5  parts  of  nickel  nitrate,  and  5  parts  of  chromium 
nitrate,  all  free  from  chlorine.  Precipitate  with  potas- 
sium carbonate,  filter,  wash,  form  into  masses  and  dry." 

The  quantity  of  nickel  can  be  varied,  for  example, 
between  the  limits  of  10  parts  and  three  parts  of  nickel 
nitrate. 

This  contact  mass  is  used  at  a  temperature  of  400° 
to  500°.C. 

As  is  true  of  all  catalysers,  the  above  appears  to 
be  subject  to  "  poisoning,"  the  chief  poisoners  being 


104     MANUFACTURE  OF  HYDROGEN 

chlorine,  bromine,  iodine,  phosphorus,  arsenic,  boron, 
and  silicon  in  some  forms  ;  hence  in  the  preparation  of 
the  catalyser,  as  well  as  in  the  manufacture  of  the  water 
gas,  precautions  must  be  taken  to  prevent  the  presence 
of  these  "  poisons  ". 

The  mixture  of  blue  water  gas  and  steam  is  passed 
over  the  catalyst  at  approximately  atmospheric  pressure. 
On  leaving  the  reaction  chamber  after  passage  through 
suitable  regenerators,  the  gas  is  compressed  to  a  pressure 
of  30  atmospheres  (441  Ib.  per  sq.  inch)  and  then  passes 
to  the  bottom  of  a  high  tower  packed  with  flints,  in 
which  it  meets  a  downward  flow  of  water  which  absorbs 
the  carbon  dioxide,  and  also  the  sulphuretted  hydrogen 
which  is  present  in  the  gas  to  a  very  slight  extent.  The 
energy  in  the  water  leaving  the  tower  is  recovered  in 
the  form  of  power  by  letting  it  impinge  on  a  Pelton 
wheel. 

The  removal  of  the  2  per  cent,  of  carbon  monoxide 
is  accomplished  in  a  similar  tower  ;  only  in  this  case 
a  solution  of  ammoniacal  solution  of  cuprous  chloride  is 
used  instead  of  water.  Given  an  adequate  size  of  tower 
and  volume  of  the  cuprous  chloride  solution,  the  pressure 
at  which  the  gas  is  introduced  into  the  tower  may  be  as 
low  as  30  atmospheres  (441  Ib.  per  sq.  inch) ;  however, 
where  the  gas  is  to  be  used  for  making  synthetic  am- 
monia it  is  usual  to  compress  it  to  200  atmospheres 
(2940  Ib.  per  sq.  inch)  before  passing  it  through  the  carbon 
monoxide  absorbing  tower.  The  use  of  this  high  pres- 
sure is  ultimately  necessary  in  the  ammonia  process  and 
it  reduces  the  size  of  the  tower  which  has  to  be  employed. 

The  cuprous  chloride  solution,  after  leaving  the  ab- 
sorption tower,  is  passed  through  a  small  vessel,  in  which 
it  gives  up  its  carbon  monoxide.  The  gas  evolved  from 


CHEMICAL    METHODS  105 

the  solution  is  passed  through  water  in  order  to  prevent 
any  ammonia  loss. 

The  advantages  of  this  process  over  the  Iron  Contact 
process  are  : —  . 

1.  It  is  continuous  in  operation. 

2.  It  is  more  economical. 

3.  The  whole  of  the  sulphur  compounds  in  the  blue 
gas  are  converted  into  sulphuretted  hydrogen  and  are 
completely  absorbed  by  the  high  pressure  water  scrub- 
bing. 

The  disadvantages  as  compared  with  the  Iron  Con- 
tact process  are : — 

1.  Greater  complexity  of  operation. 

2.  For  aeronautical  purposes  the  percentage  of  nitro- 
gen is  high. 

Description  of  Plant --The  diagram  (Fig.  12) 
shows  the  method  of  operation  of  this  process.  Steam 
enters  by  the  pipe  A  and  mixes  with  blue  water  gas 
entering  by  the  pipe  B,  the  speed  of  flow  of  each  being 
indicated  on  separate  gauges  as  shown.  The  mixture  of 
steam  and  gas  passes  through  the  regenerator  or  super- 
heater C  and  flows,  as  indicated  by  the  arrows,  over 
refractory  tubes,  through  which  the  hot  products  of  the 
reaction  are  flowing  in  the  reverse  direction.  The  heated 
mixed  gases  flow  via  the  pipe  F  into  the  generator  and, 
increasing  in  temperature,  pass  through  the  catalytic 
material,  where  reaction  takes  place  with  the  evolution 
of  heat.  They  then  flow  as  indicated  by  the  arrows 
back  through  the  regenerator,  parting  with  their  heat  to 
the  incoming  mixture  of  blue  water  gas  and  steam. 

Thermo-couples  are  placed  in  the  contact  mass  so 
that  its  temperature  may  be  controlled  by  increasing  or 


io6 


MANUFACTURE  OF  HYDROGEN 


reducing  the  quantity  of  steam  in  the  incoming  gaseous 
mixture. 

The  whole  apparatus  is  very  effectively  lagged  to 
reduce  the  heat  losses  to  a  minimum. 

To  Ml  Hi  -  voltmeter 


Superheater  or 
Regenerator 


Water  Gas 
Inlet 


Orifice  Gauge 


Thermo  -couples 
for  Temperatures 
between  4-50  &  500°  C 
G 


Contact 
Material 


Orifice 
Gauge 
(Hg) 


Hydrogen 

anclC02 

Outlet 


Diatomite  Brick  Cover 
throughout*  bound  with 
Painted  Cloth 


To  Milli- 
voltmeter 


FIG.  12. 

The  following  patents  on  this  process  by  the  Badische 
Analin  and  Soda  Fabrik  are  in  existence  :— 

English  patent     27117.      1912. 

27963.      1913. 

French        ,,       4599 1 8.      1913. 


CHEMICAL   METHODS  107 

The  following  patents  relating  to  the  general  chemi- 
cal reaction  in  this  process  have  been  taken  out : — 

Tessie  du  Motay.  U.S.     patent   229338.  1880. 

229339.  1880. 

229340.  1880. 

Pullman  &  Elworthy.        English     ,,         22340.  1891. 

Elworthy.  French      „      355324-  1905- 

Ellis  &  Eldred.  U.S.          „       854157.  1907. 

Chem.  Fabrik  Greisheim 

Elektron.  British        „  2523.      1909. 

Naber  &  Muller.  German     ,,       237283.      1910. 

Using  Lime. — If  carbon  monoxide  together  with 
steam  is  passed  over  lime  at  a  temperature  of  about 
500°  C,  the  monoxide  is  absorbed  with  the  formation  of 
calcium  carbonate,  and  hydrogen  is  evolved  in  accord- 
ance with  the  following  equation  : — 

CaO  +  H2O  +  CO  =  CaCO3  +  H2. 

Investigation  of  the  above  reaction  by  Levi  &  Piva1 
indicates  that  the  chemical  change  takes  place  in  two 
stages,  in  the  first  of  which  calcium  formate  is  produced, 
while  in  the  second  it  is  decomposed  with  the  evolution 
of  hydrogen  and  carbon  monoxide  as  is  shown  in  the 
following  equations : — 

(1)  CaO  +  H,O  +  2CO  =  Ca(COOH)2, 

(2)  Ca(COOH)2  =  CaC03  +  CO  +  H2. 

It  can,  however,  be  seen  from  these  equations  that 
whatever  volume  of  carbon  monoxide  is  permanently 
absorbed,  an  equal  volume  of  hydrogen  is  evolved. 

Now,  since  blue  water  gas  is,  roughly  speaking,  half 
hydrogen  and  half  carbon  monoxide,  by  passing  it  over 

1  "  Journ.  Soc.  Chem.  Ind.,"  1914,  310. 


io8     MANUFACTURE  OF  HYDROGEN 

lime  under  the  conditions  stated  above,  a  gas  equal  in 
volume  to  the  water  gas,  but  wholly  composed  of  hydro- 
gen, is  produced. 

In  the  commercial  operation  of  this  process,  the  lime 
is  contained  in  a  tower,  which  is  initially  heated  to  a 
temperature  of  about  500°  C.,  but  since  the  absorption 
of  the  carbon  monoxide  is  exothermic,  after  the  process 
has  started,  no  further  heating  is  required. 

When  the  lime  has  become  sluggish  in  its  action,  by 
the  formation  of  a  crust  of  calcium  carbonate,  the  blue 
gas  is  diverted  through  a  similar  tower,  while  the  con- 
tents of  the  original  tower  are  heated  in  situ  to  a  tem- 
perature sufficiently  great  to  decompose  the  calcium 
carbonate,  and  thus  the  tower  is  again  ready  for  use. 

This  process  is  protected  by  the  following  patents  : — 

Chem.  Fabrik  Greisheim 

Elektron.  British  patent  2523.  1909. 

Dieffenbach  &  Molden- 

hauer.  ,,  ,,  8734.  1910. 

Ellenberger.  U.S.  ,,  989955.  1912. 

Chem.  Fabrik  Greisheim 

Elektron.  British       ,,         13049.      1912. 

(4)  Miscellaneous  Methods  of  Making  Hydrogen* 

THE  CARBONIUM  GESELLSCHAFT  PROCESS. 

From  Acetylene* — If  acetylene  is  compressed  and 
then  subjected  to  an  electric  spark  it  undergoes  dis- 
sociation into  its  elements. 

Acetylene  can  be  most  easily  generated  from  the 
action  of  water  on  calcium  carbide,  thus  :— 

CaQ,  +  2H2O  =  C2H2  +  Ca(OH)2. 


CHEMICAL    METHODS  109 

The  acetylene  produced  is  then  compressed  in  very 
strong  cylinders  and  subjected  to  an  electric  spark,  when 
the  following  reaction  takes  place  :— 
C2H2  =  C2  +  H2. 

If  the  acetylene  is  produced  from  calcium  carbide, 
approximately  178  Ib.  of  calcium  carbide  and  100  Ib.  of 
water  are  theoretically  required  to  produce  1000  cubic 
feet  of  hydrogen  at  40°  F.  and  30  inches  barometer, 
while,  at  the  same  time,  39  Ib.  of  carbon  in  the  form  of 
lamp-black  is  produced. 

This  process  is  employed  by  the  Carbonium  Gesell- 
schaft  of  Frederickshaven  for  the  inflation  of  airships, 
while  the  carbon  produced  is  sold  and  is  used  in  making 
printers'  ink.  As  used  by  this  company,  the  gas  is 
compressed  to  about  i  atmospheres  (29*4  Ib.  per  sq. 
inch)  prior  to  sparking. 

The  following  patent,  relative  to  this  process,  is  in 
existence :- — 

Bosch.  German  patent  268291.      1911. 

The  decomposition  of  acetylene  may  be  obtained  by 
heating  ;  thus,  if  acetylene  derived  from  calcium  carbide 
or  some  other  source  is  passed  through  a  tube  heated  to 
about  500°  C.  it  decomposes,  in  accordance  with  the 
following  equation,  with  the  evolution  of  heat  :— 

C/2H2  =  C2  4*  H2« 

Such  is  the  quantity  of  heat  liberated  that  after  the 
temperature  of  the  tube  has  been  raised  until  decom- 
position of  the  acetylene  begins  no  further  external  heat 
is  required. 

The  carbon  produced  may  be  chiefly  removed  by 
filtering  the  gas,  while  the  residue  which  still  remains 
may  be  removed  by  scrubbing  with  water. 


no  MANUFACTURE  OF  HYDROGEN 

This  process  is  protected  by  the  following  patents  : — 

Picet.   French  patent    421838.  1910. 

421839. 

English       ,,          24256.  1910. 

German      „       255733.  1912. 

From  Hydrocarbon  Oils. — While  the  decomposition 
of  acetylene  is  attended  with  the  evolution  of  heat,  most 
other  hydrocarbon  gases  absorb  heat  when  they  decom- 
pose into  their  constituents  ;  consequently,  to  produce 
hydrogen  from  other  hydrocarbon  gas  or  volatilised 
hydrocarbon  oils,  it  is  necessary  to  supply  heat  during 
the  process. 

The  necessary  heat  may  be  supplied  by  passing  the 
hydrocarbon  gas  or  vaporised  oil  through  a  tube  of  re- 
fractory material  which  is  externally  heated,  or  the  in- 
genious Rincker-Wolter  method  may  be  used.  In  this 
process  the  rough  principle  is  to  use  a  generator  similar 
to  a  " blue-gas"  generator  filled  with  coke.  By  means 
of  an  air  blast  the  temperature  of  the  coke  is  raised  to 
about  1200°  C.,  then,  when  this  temperature  has  been 
reached,  the  air  supply  is  stopped  and  crude  oil  is  blown 
in  at  the  bottom  of  the  hot  coke. 

The  oil  is  immediately  volatilised,  and  passes  by  ex- 
pansion up  through  the  hot  coke,  during  which  process 
it  is  decomposed  into  hydrogen  and  carbon,  the  latter 
to  a  large  extent  attaching  itself  to  the  coke  and  becom- 
ing a  source  of  fuel.  When  the  temperature  has  fallen 
too  low  to  effect  a  complete  decomposition  of  the  crude 
oil  the  injection  is  stopped  and  the  temperature  of  the 
coke  again  raised  by  means  of  the  air  blast.  The  gas 
produced  by  this  process  is  stated  to  have  the  following 
composition  : — 


CHEMICAL   METHODS 


in 


Hydrogen  . 
Nitrogen  . 
Carbon  monoxide 


Per  Cent. 

by  Volume. 

96*0 

•         I'3 

27 


The  cost  of  hydrogen  made  by  this  process  must 
depend  almost  entirely  on  the  price  of  crude  oil ;  it  is 
stated  that,  with  crude  oil  at  twopence  a  gallon,  hydro- 
gen can  be  produced  for  about  seven  shillings  a  thousand 
cubic  feet.1 

The  following  patents  deal  with  this  or  somewhat 
similar  processes : — 


Geisenberger. 
Rincker  &  Wolter. 

»>  >» 

Berlin  Anhaltische 
Maschinenbau  A.  G 


C.  Ellis. 


French  patent      361462.     1905. 

391867.  1908. 

391868.  1908. 


German 
French 
English 
U.S. 


267944.  1913. 

466040.  1913. 

2054.  1914. 

1092903.  1914. 


From  Starch.  —  When  yeast,  which  is  a  living 
organism,  is  introduced  into  a  solution  containing 
sugar,  fermentation  results  with  the  production  of 
alcohol  and  carbon  dioxide,  which  may  be  expressed  in 
an  equation  as  follows  :— 

C12H22On  +  H2O  =  4C2H6O  +  4CO2. 

An  analogous  process  to  the  above  is  employed 
commercially  for  the  production  of  acetone  and  butyl 
alcohol. 

When  what  is  known  as  the  Fernbach  bacillus  is  in- 
troduced into  starch  jelly,  #(C6HIOO5),  acetone,  (CH3)2CO, 

1  Ellis,  "The  Hydrogenation  of  Oils"  (Constable). 


ii2     MANUFACTURE  OF  HYDROGEN 

and  butyl  alcohol,  CH3CH2CH2CH2OH,  are  produced  ; 
at  the  same  time  there  is  an  evolution  of  gas  which  is 
chiefly  hydrogen  and  carbon  dioxide,  but  it  also  con- 
tains a  little  nitrogen. 

As  there  is  a  great  demand  for  acetone  in  certain 
localities,  large  quantities  of  hydrogen  in  this  impure 
form  are  being  produced  as  a  by-product.  If  the 
carbon  dioxide  is  absorbed  by  passing  the  gas  under 
pressure  through  water  (Bedford  method),  a  gas  is  pro- 
duced of  about  the  following  composition  : — 

Hydrogen    ........     94*0 

Nitrogen 6*0 

The  above  is  not  a  process  for  the  production  of 
hydrogen,  but  the  hydrogen  produced  may  be  frequently 
usefully  employed  if  there  is  a  local  demand  for  it. 


CHAPTER  IV. 

THE    MANUFACTURE   OF   HYDROGEN. 

CHEMICO-PHYSICAL  METHODS. 

Linde'Frank'Caro  Process* — The  most  important 
method  of  producing  hydrogen,  in  which  chemical  and 
physical  methods  are  employed,  is  one  in  which  the 
chemical  process  results  in  the  production  of  blue  water 
gas,  and  the  physical  in  the  separation  of  the  chemical 
compounds  (chiefly  carbon  monoxide)  from  the  hydrogen 
by  liquefaction. 

THE  SEPARATION  OF  HYDROGEN  FROM  BLUE  WATER 

GAS. 

The  separation  of  mixed  gases  by  liquefaction  is 
a  subject  of  very  great  complexity  and  one  into  the 
intricacies,  of  which  it  is  not  intended  to  go  in  this  work, 
but  for  further  information  the  attention  of  the  reader 
is  directed  to  the  two  following  books  :— 

"The  Mechanical  Production  of  Cold,"  by  J.  A. 
Ewing.  (Cambridge  University  Press.) 

"  Liquid  Air,  Oxygen,  Nitrogen,"  by  G.  Claude. 
(J.  &  A.  Churchill.) 

All  gases  are  capable  of  being  liquefied,  but  in  the 
case  of  hydrogen  and  helium l  the  difficulties  are  so  great 

1  This  gas,  which  was  the  last  to  resist  liquefaction,  was  first 
liquefied  on  xoth  July,  1908,  by  Professor  Kamerlingh-Onnes. 

(U3)  8 


114 


MANUFACTURE  OF  HYDROGEN 


that  it  is  only  by  means  of  the  highest  technical  skill  and 
very  costly  apparatus  that  this  can  be  accomplished. 

Originally  it  was  considered  that  to  obtain  a  gas  in 
the  liquid  state  the  sole  necessity  was  pressure  ;  how- 
ever, all  gases  possess  a  physical  property  known  as 
critical  temperature^  The  critical  temperature  of  a 
gas  is  that  temperature  above  which  the  gas  cannot  be 
liquefied,  however  great  the  pressure  to  which  it  is  sub- 
jected. 

Prior  to  the  realisation  of  the  existence  of  the  critical 
temperature,  chemists  and  physicists  subjected  various 
gases  to  enormous  pressures  in  the  hope  of  causing  them 
to  liquefy,  and,  though  they  failed,  it  is  interesting  to 
observe  from  the  accounts  of  their  experiments  that  the 
compressed  gas  attained  a  density  greater  than  the 
same  gas  in  the  liquid  state  at  atmospheric  pressure. 

Besides  critical  temperature,  another  term  requires 
definition,  that  is,  critical  pressure,  which  is  the  pressure 
which  must  be  exerted  on  a  gas  cooled  to  its  critical 
temperature  to  produce  liquefaction. 

The  following  table  of  critical  temperatures  and 
pressures  of  the  constituents  of  blue  water  gas  is  interest- 
ing :— 


Gas. 

Critical 
Temperature. 

Critical  Pressure. 

Hydrogen  . 
Carbon  monoxide 
,,       dioxide  . 
Nitrogen     . 
Methane    . 

-  234-0°  C. 
-  136*0 

+   30-92 

-   146-0 

-    82-0 

294  lb.  per  sq.  in. 
492 
H31 
485 
820 

Sulphuretted  hydrogen 
Oxygen 

+     lOO'O 

-   118-0 

i304 

735 

1  Discovered  by  Andrews,  1863. 


CHEMICO-PUYSICAL  METHODS  115 

From  this  table  it  is  seen  that  the  critical  tempera- 
ture of  hydrogen  is  88°  C.  below  that  of  its  nearest 
associate,  nitrogen  ;  consequently,  if  the  blue  water  gas 
were  cooled  to  —  146°  C.  while  subjected  to  a  pressure  of 
somewhere  about  500  Ib.  per  square  inch,  the  whole  of 
the  gas,  with  the  exception  of  the  hydrogen,  would 
liquefy  ;  therefore,  separation  of  a  liquid  from  a  gas 
being  a  simple  matter,  the  problem  of  the  production  of 
hydrogen  from  blue  water  gas  would  be  solved. 

If  a  gas  is  cooled  below  its  critical  temperature  the 
pressure  which  has  to  be  applied  to  produce  liquefaction 
is  much  reduced.  Now,  since  the  boiling  point  of  a 
liquid  and  the  condensing  point  of  a  vapour  under  the 
same  pressure  are  the  same  temperature,  the  boiling 
points  of  the  various  gases  contained  in  blue  water  gas 
can  be  studied  with  advantage. 

BOILING  POINTS  OF  SOME  LIQUID  GASES  AT  ATMOS- 
PHERIC PRESSURE. 

Gas.  Boiling  Point. 

Hydrogen -  253-0°  C. 

Carbon  monoxide      .         .         .         .  -  190*0 

„       dioxide -     So-o 

Nitrogen  .         .         .         .         .         .  -  195*5 

Methane -  1647 

Sulphuretted  hydrogen        .         .         .  -     61-6 

Oxygen -  182-5 

Therefore,  it  can  be  seen  that,  if  blue  water  gas 
were  cooled  at  atmospheric  pressure  to  a  temperature 
below  —  195*5°  C->  tne  whole  of  the  constituents  of  the 
gas,  other  than  hydrogen,  would  be  liquefied,  and  con- 
sequently an  easy  separation  could  be  made. 

To  summarise,  the  liquefaction  of  the  constituents  of 


ii6     MANUFACTURE  OF  HYDROGEN 

blue  water  gas,  other  than  hydrogen,  can  be  accom- 
plished either  by  a  moderate  degree  of  cooling  and  the 
application  of  pressure,  or  by  intense  cooling  and  no 
application  of  pressure. 

PRODUCTION  OF  HYDROGEN  FROM  WATER  GAS  BY  THE 
LINDE  PROCESS. 


H2S  C02  CH4  CO  N2  H2 

phuretted    Carbon  Methane      Carbon  Nit  H  d 

ydrogen.    Dioxide.  Monoxide. 

•5%  3'5°/o          -4%  39-6%  4%  52% 


Oxide  Boxes.     H2S  partly  absorbed. 

Compressor.     20  Atmospheres  (294  lb./Q"). 

Pressure  Water  Scrubber.     CO2  &  H<2S  almost  entirely  absorbed. 

Caustic  Soda  Scrubber  (NaOH  30%),  last  traces  CO2  &  H2S  absorbed. 


Ammonia  Cooler.     Water  Vapour  condensed, 
Temperature  reduced  to  -  25°  C. 


Linde  Still.     Final  Temperature  -  205°  C. 
Methane,  Carbon  Monoxide  &  Nitrogen  liquified. 


I  I 

Gaseous  Hydrogen  Methane,  Carbon  Monoxide 

^2         97%  by  Volume.  &  Nitrogen.     On  evapora- 

CO          2  „         „  tion  to  gas  engine  operat- 

N2           i ,,         ,,  ing  the  whole  plant. 

In  the  Linde- Frank-Caro  process  the  blue  water 
gas  is  compressed  to  20  atmospheres,  and  under 
pressure  it  is  passed  through  water,  which  removes 


CHEMICO-PHYSICAL  METHODS  117 

practically  the  whole  of  the  carbon  dioxide  and  sul- 
phuretted hydrogen.  It  is  then  passed  through  tubes 
containing  caustic  soda,  which  removes  the  remaining 
traces  of  carbon  dioxide,  sulphuretted  hydrogen,  and 
water. 

The  gas  thus  purified  from  these  constituents  now 
passes  to  the  separator  proper  ;  the  reason  for  this  pre- 
liminary removal  of  some  of  the  constituents  of  the  blue 
water  gas  is  due  to  the  fact  that,  in  the  separation  of  the 
carbon  monoxide  and  nitrogen,  such  low  temperatures 
have  to  be  reached  that  the  water,  sulphuretted  hydrogen, 
and  carbon  dioxide  would  be  in  the  solid  state,  and 
would,  therefore,  tend  to  block  up  the  pipes  of  the  ap- 
paratus. 

The  apparatus  operates  in  the  following  manner, 
which  will  be  more  readily  understood  by  consulting  the 
diagram  (Fig.  13):- 

The  purified  water  gas  passes  down  the  tube  A, 
through  coils  in  the  vessel  B,  which  is  filled  with 
liquid  carbon  monoxide  boiling  at  atmospheric  pressure 
(  -  190°  C.).  Now,  since  the  water  gas  is  under  pres- 
sure and  is  passing  through  coils  cooled  to  its  tempera- 
ture of  liquefaction  at  atmospheric  pressure,  the  bulk  of 
it  liquefies  (theoretically  more  gas  should  be  liquefied  in 
the  tubes  than  is  evaporated  outside  them). 

The  gas,  containing  a  considerable  amount  of  liquid 
saturated  with  hydrogen,  passes  into  the  vessel  C, 
which  is  surrounded  by  liquid  nitrogen  boiling  under 
reduced  pressure  giving  a  temperature  of  —  205°  C. 
Here  the  remainder  of  the  carbon  monoxide  and  the 
nitrogen  originally  contained  in  the  gas  liquefies  and 
hydrogen  of  approximately  the  following  composition 
passes  up  the  tube  E  :— 


u8 


MANUFACTURE  OF   HYDROGEN 


A.  Water  Gaslntet.  A.    ^ 


D  .Nitrogen  Outlet  D. 


Carbon  Monoxide  Outlet 


/  iquid  Nitrogen  Inlet 


B 


\G 


FIG.  13. — Diagram  showing  Linde-Frank-Caro  Process. 


1  Hydrogen  . 
Nitrogen 

Carbon  monoxide 
Sulphuretted  hydrogen  . 
Organic  sulphur  compounds 


Per  Cent, 
by  Volume. 
.      97-0 
I'O 

2'0 

nil. 


When  the  gas  is  required  to  be  of  high  purity  it  is 

1  Messrs.  Ardol  of  Selby,  Yorks,  who  employ  this  process,  kindly 
supplied  the  author  with  this  information. 


CHEMICO-PHYSICAL  METHODS  119 

subsequently  passed  over  calcium  carbide  or  soda  lime, 
the  reactions  of  which  processes  will  be  dealt  with  later. 

During  the  operation  of  the  process  liquid  carbon 
monoxide  and  some  liquid  nitrogen  collects  in  C. 
Now  this  liquid  gas  is  under  pressure  and  can  therefore 
be  run  back  through  the  tube  F  via  the  cock  G 
into  the  vessel  B  ;  but  B  is  at  atmospheric  pressure, 
consequently  some  of  the  liquid  gas  passing  through  G 
will  be  volatilised,  with  consequent  fall  in  tempera- 
ture of  the  remainder. 

The  liquid  nitrogen  used  in  the  vessel  D  is  pro- 
duced in  a  special  Linde  machine  from  the  atmosphere. 

The  vapour  of  carbon  monoxide,  with  a  little 
nitrogen  and  hydrogen,  from  the  vessel  B  is  used  to 
cool  the  incoming  purified  water  gas,  as  is  shown  in  the 
diagram.  This  method  of  using  the  cold  separated 
gases  for  cooling  the  gas  going  into  the  apparatus  is 
termed  "  Cooling  by  counter-current  heat  exchangers," 
and  it  may  be  regarded  as  the  essence  of  efficiency  in 
all  low  temperature  gas  separation. 

The  consumption  of  power  in  this  process  is  theo- 
retically very  small,  as  much  carbon  monoxide  should 
be  liquefied  in  the  coil  in  the  vessel  B  as  is  volatilised 
outside  it  (this  is  theoretically  true  when  the  pressure 
of  the  gas  passing  through  the  coil  is  atmospheric). 
However,  in  practice,  the  necessity  for  power  consump- 
tion arises  from  the  fact  that  liquid  nitrogen  must 
be  continuously  supplied  to  the  vessel  D  in  order  to 
prevent  the  temperature  of  the  plant  rising  from  ex- 
ternal infiltration  of  heat,  which  takes  place  in  spite  of 
the  most  effective  lagging. 

In  practice,  the  power  obtained  from  using  the  sepa- 
rated carbon  monoxide  as  a  fuel  is  sufficient  to  run  all 


120  MANUFACTURE  OF  HYDROGEN 

the  machines  necessary  for  the  operation  of  a  plant  pro- 
ducing 3500  cubic  feet  of  hydrogen  or  more  per  hour. 

Thus,  to  very  roughly  indicate  the  cost  of  operation 
of  this  process,  neglecting  all  depreciation,  etc.,  it  may 
be  said  that,  on  a  plant  of  the  size  mentioned  above, 
unit  volume  of  blue  water  gas  yields  '4  volume  of 
hydrogen  of  about  97  per  cent,  purity,  or,  on  the  basis 
of  a  coke  consumption  of  35  Ib.  per  1000  cubic  feet  of 
water  gas,  the  hydrogen  yield  is  25,500  cubic  feet  per 
ton  of  coke. 

Purification  of  Hydrogen. — Where  very  pure 
hydrogen  is  required  it  is  necessary  to  employ  chemical 
methods  to  remove  the  3  per  cent,  of  impurity,  which 
may  be  done  by  passing  the  gas  through  heated  soda 
lime,  where  the  carbon  monoxide  is  absorbed  in  accord- 
ance with  the  following  equation  : — 

2NaOH  +  CO  =  Na2CO3  +  H2, 

or,  on  the  other  hand,  it  may  be  passed  through  heated 
calcium  carbide  (over  300°  C.),  which  possesses  the 
advantage  of  not  only  removing  the  carbon  monoxide 
but  also  the  nitrogen.  The  reactions  taking  place  are 
indicated  in  the  following  equations  :— 

CaC2  +  CO  =  CaO  +  sQ 
CaC2  +  N2  =  CaCN2  +  C. 

The  following  is  given  as  an  analysis  of  the  gas 
purified  by  means  of  soda  lime  : — 

Per  Cent, 
by  Volume. 
Hydrogen      .......     99'2-99'4 

Carbon  monoxide  .....  nil. 

Nitrogen o'8-o*6 

The  following  patents  are  in  existence  for  the  pro- 


CHEMICO-PHYSICAL  METHODS 


21 


duction  of  hydrogen  by  liquefaction  methods  from  blue 
water  gas :  — 

Elworthy. 


Frank. 

Claude. 

Ges-fur  Linde's  Eis- 

maschinen  A.G. 
C.  von  Linde. 


Chemical  purification- 
Frank. 


French  patent  355324-  ^OS- 
English  ,,  26928.  1906. 
French  „  3  7  599 1.  1906. 


U.S. 


French 


417983.  1911. 

1020102.  1912. 

1020103.  1912. 

1027862.  1912. 

1027863.  1912. 

371814.  1906. 


Diffusion* — The  separation  of  hydrogen  from  the 
other  constituents  of  blue  water  gas  has  been  proposed, 
employing  diffusion  for  the  purpose.  Graham  expressed 
the  law  of  diffusion  of  gases  as  : — 

"  The  relative  velocities  of  diffusion  of  any  two 
gases  are  inversely  as  the  square  roots  of  their  densities." 

That  is  to  say,  if  a  mixture  of  two  gases  of  different 
densities  is  passed  through  a  porous  tube,  e.g.  unglazed 
porcelain,  in  a  given  time,  more  of  the  lighter  gas  would 
have  passed  through  the  walls  of  the  tube  than  of  the 
heavier,  or,  to  take  a  concrete  example,  suppose  the 
mixture  of  gases  was  one  composed  of  equal  parts  by 
volume  of  hydrogen  and  oxygen,  then,  since  their 
densities  are  as  i  to  16,  and  since,  therefore,  the  roots 
of  their  densities  are  as  i  to  4,  in  a  given  time  four 
times  as  much  hydrogen  would  diffuse  through  the 
medium  as  oxygen. 

The  densities  and  the  square  roots  of  the  densities 
of  the  constituents  of  blue  water  gas  are  given  below  : — 


22 


MANUFACTURE  OF  HYDROGEN 


Density. 

X/D. 

Hydrogen  .... 

I 

i 

Carbon  monoxide 

U 

3*7 

,,        dioxide   . 

22 

47 

Nitrogen     .... 

14 

37 

Methane    .... 

8 

2-8 

Sulphuretted  hydrogen 

17 

4'i 

Oxygen        .... 

16 

4-0 

From  which  it  will  be  seen  that,  if  blue  gas  were 
passed  continuously  through  a  porous  tube,  the  gas  dif- 
fusing through  the  tube  would  contain  more  hydrogen 
than  the  blue  gas  originally  contained.  Of  course,  in 
the  successful  operation  of  a  diffusion  separation  it  is 
necessary  to  remove  the  gas  which  diffuses  through  the 
porous  medium  as  well  as  the  residue  which  is  left  un- 
diffused.  The  former  may  be  done  by  maintaining  a 
constant  pressure  by  means  of  a  suction  pump,  while 
the  latter  can  be  done  by  regulating  the  speed  of  flow 
through  the  diffusion  tube.  It  is,  of  course,  essential 
that  the  undiffused  gas  must  be  removed  from  contact 
with  the  porous  medium  after  a  certain  time,  as  it  is  only 
a  matter  of  time  before  the  whole  of  the  gas  will  diffuse 
through  the  medium,  and  thus  destroy  the  work  of 
separation. 

THE  DIFFUSION  MEDIUM. 

The  selection  of  the  diffusion  material  is  a  subject 
of  considerable  difficulty  ;  if  the  porosity  of  the  material 
is  too  great  no  diffusion  takes  place,  but  the  gas  passes 
through  the  material  without  any  appreciable  separation 
taking  place.  Thus,  if  a  mixture  of  hydrogen  and 
oxygen  is  passed  through  a  fine  capillary  tube,  the  gas 


CHEMICO-PHYSIC AL  METHODS  1 23 

issuing  will  be  found  to  be  of  the  same  composition  as 
the  original  gas. 

It  is  interesting  to  note  in  this  connection  that,  if 
pure  hydrogen  were  first  passed  through  the  tube  and 
then  pure  oxygen,  in  a  given  time  more  hydrogen  by 
volume  would  pass  through  the  tube  than  oxygen. 
This  differential  rate  of  flow  through  tubes  is  called 
"  Transpiration  ". 

If  the  porosity  of  the  material  is  insufficient,  the  time 
required  to  effect  separation  is  unduly  long.  It  may,  in 
this  connection,  be  mentioned  that  it  has  from  time  to 
time  been  suggested  that  by  means  of  diffusion  it  would 
be  possible  to  separate  a  mixture  of  gases  of  different 
densities  without  the  consumption  of  power.1  How- 
ever, in  practice  this  has  not  been  found  to  be  the  case, 
as,  in  order  to  obtain  a  reasonable  speed  of  separation, 
a  difference  of  pressure  between  the  two  sides  of  the 
diffusion  material  has  to  be  maintained. 

Jouve  and  Gautier  have  employed  a  diffusion 
method  in  order  to  separate  hydrogen  from  blue  water 
gas,  and  it  is  stated  that,  by  a  single  passage  through  a 
porous  partition,  the  percentage  of  carbon  monoxide  in 
the  gas  passing  through  the  medium  was  reduced  from 
45  per  cent,  in  the  original  gas  to  8  per  cent.  Whether 
this  process  has  been  employed  on  a  commercial  scale 
is  not  known  to  the  author,  nor  has  he  any  knowledge 
as  to  the  amount  of  power  required  to  obtain  a  definite 
volume  of  hydrogen  practically  free  from  carbon  mon- 
oxide. 

The  following  patents,  in  which  diffusion  has  been 

1  It  is  theoretically  impossible  to  separate  a  mixture  of  two  gases 
without  the  consumption  of  power,  but  the  theoretical  requirements 
are  almost  negligible. 


124     MANUFACTURE  OF  HYDROGEN 

employed  for  separating  mixed  gases,  have  been  taken 

out  :— 

Jouve  &  Gautier-     French  patent    372045.      1908 
Hoofnagle.  U.S.  ,,      1056026.      1913 

Separation  by  Centrifugal  Force, — When  a  mass  is 
compelled  to  move  in  a  circular  course  a  force  acts  on  it 
which  is  a  function  of  its  mass,  linear  velocity,  and  the 
radius  of  curvature  of  its  path,  which  may  be  expressed 
as— 

„        .f  m .  v* 

Centrifugal  force  =  — =— 

Jx 

where  m  =  mass  of  the  body, 
v  =  its  linear  velocity, 
R  =  the  radius  of  curvature  of  its  path. 

Therefore,  since  a  greater  force  is  acting  on  the  heavier 
of  two  particles  moving  on  the  same  course  with  the 
same  velocity,  the  heavier  particle  will  tend  to  move 
outward  from  its  centre  of  rotation  to  a  greater  extent 
than  the  lighter.  This  principle  of  centrifugal  force  is 
employed  industrially  for  many  purposes,  such  as  the 
separation  of  cream  from  milk,  water  from  solid  bodies, 
honey  from  the  comb,  etc.,  and  it  has  been  suggested 
that  it  might  be  used  to  separate  hydrogen  from  blue 
water  gas.  However,  though  a  certain  amount  of  work 
has  been  done  on  this  problem  by  El  worthy l  and 
Mazza,2  as  far  as  the  author  knows  no  satisfactory  results 
have  been  obtained. 

The  special  physical  questions  involved  in  the  sepa- 
ration of  gases  of  different  densities  by  means  of  a 
centrifugal  machine  have  been  considered  theoretically 

1  Elworthy,  English  patent,  1058.     1906. 

2  Mazza,  English  patent,  7421.     1906. 


CHEMICO-PHY5ICAL  METHODS  125 

by  a  number  of  physicists,  whose  conclusions  are  that 
very  high  velocities  must  be  given  to  the  gas  to  obtain 
any  appreciable  separation  ;  it  has  been  shown  that,  if  a 
drum  3  feet  in  diameter  and  one  foot  long  filled  with  a 
mixture  at  15°  C.,  containing  80  per  cent,  of  hydrogen 
and  20  per  cent  of  air,  is  rotated  at  20,000  revolutions 
per  minute,  a  condition  of  dynamical  equilibrium  will 
arise  when  the  peripheral  gas  and  the  axial  gas  will 
have  the  following  composition  : — 

Axial  Gas.         Peripheral  Gas. 

Hydrogen        .         ...       97-8  66' i 

Air          .....         2-2  33-9 

Since  the  density  of  air  and  that  of  carbon  monoxide 
are  almost  the  same  (14*4  and  14*0)  almost  identical 
theoretical  results  could  be  obtained  by  giving  a  similar 
rotary  motion  to  a  mixture  of  80  per  cent,  hydrogen  and 
20  per  cent,  carbon  monoxide.  However,  the  enormous 
speed  of  rotation  and  a  practical  method  of  removing  the 
axial  and  peripheral  gases  makes  this  question  one  of  the 
greatest  technical  difficulty,  and  it  may  well  be  that  the 
power  consumption  to  produce  a  given  volume  of  hydro- 
gen from  blue  water  gas  may  be  greater  than  that 
required  to  produce  an  equal  volume  of  hydrogen  by 
electrolysis. 


CHAPTER  V. 
THE  MANUFACTURE  OF  HYDROGEN. 

PHYSICAL  METHODS. 

Electrolysis* — When  an  electric  current  passes 
through  a  solid  conductor  a  magnetic  field  is  created 
round  the  conductor  and  the  conductor  is  heated  by  the 
passage  of  the  current,  both  of  which  effects  bear  a 
definite  relationship  to  the  magnitude  of  the  current 
passing.  Some  liquids  are  also  conductors  of  electricity, 
e.g.  mercury  ;  the  passage  of  a  current  through  such  a 
conductor  produces  results  identical  with  those  produced 
in  solid  conductors.  Other  liquids  are  also  conductors, 
but,  besides  the  passage  of  the  current  creating  a  mag- 
netic field  and  a  heating  effect,  a  portion  of  the  liquid  is 
split  up  into  two  parts  which  may  each  be  a  chemical 
element,  or  one  or  either  may  be  a  chemical  group. 

Thus,  if  two  platinum  plates  are  placed  as  shown  in 
the  diagram,  one  plate  being  connected  to  the  positive 
pole  of  the  battery  and  the  other  to  the  negative,  then, 
if  a  strong  aqueous  solution  of  hydrochloric  acid  is  put  in 
the  vessel  containing  the  plates,  decomposition  of  the 
liquid  will  take  place  :  hydrogen  will  be  given  off  at  the 
negative  plate  or  cathode,  and  chlorine  at  the  positive 
or  anode. 

If  the  solution  of  hydrochloric  acid  is  replaced  by  one 

of  caustic  soda  the  caustic  soda  is  split  up  by  the  current 

(126) 


PHYSICAL  METHODS 


127 


into  oxygen,  which  is  liberated  at  the  anode,  and  metallic 
sodium  which  is  deposited  on  the  cathode  ;  but  since 
metallic  sodium  cannot  exist  in  contact  with  water,  the 
following  reaction  takes  place  at  the  cathode  :— 


2Na  +  2H2O  = 


H 


Thus,  by  a  secondary  reaction,  hydrogen  is  liber- 
ated at  the  cathode,  or,  in  other  words,  water  is  split  into 
its  constituents,  while  the  caustic  soda  is  reformed. 

Now,  let  the  caustic  soda  solution  be  replaced  by  an 
aqueous  solution  of  sulphuric  acid.  In  this  case  hydro- 
gen will  be  liberated  at  the  cathode  and  the  group  SO4 
at  the  anode,  but  the  group  SO4  cannot  exist  in  contact 
with  water,  as  the  following  reaction  takes  place  :  — 


2SO4 


=  2H2SO4  +O2. 


Thus,  by  a  secondary  reaction,  oxygen  is  liberated 
at  the  anode,  or,  in  other  words,  water  is  split  into  its 
constituents  while  the  sulphuric  acid  is  reformed. 


<Xj                                                           «Vi 

^                  ^ 

<:                                         ^ 

^ 

^        Electrolyte 

Hl|ll|l- 

Battery 

FIG.   14. — Electrolytic  Cell. 

Liquids  which,  under  the  influence  of  the  electric 
current,  behave  in  the  manner  of  the  above  are  termed 
"  Electrolytes,"  and  the  process  whereby  they  are  split 
up  is  called  "  Electrolysis  ". 


128 


MANUFACTURE  OF   HYDROGEN 


The  laws  relating  to  this  decomposition  of  liquids 
by  the  electric  current  were  enunciated  by  Faraday  as 
follows  :• — 

1.  The  quantity  of  an  electrolyte  decomposed  is  pro- 
portional to  the  quantity  of  electricity  which  passes. 

2.  The  mass  of  any  substance  liberated  by  a  given 
quantity  of  electricity  is  proportional  to    the  chemical 
equivalent  weight  of  the  substance. 

By  the  chemical  equivalent  weight  of  a  substance  is 
meant  in  the  case  of  elements,  the  figure  which  is  ob- 
tained by  dividing  its  atomic  weight  by  its  valency, 
while  in  the  case  of  compounds,  it  is  the  molecular 
weight  divided  by  the  valency  of  the  compound.  How- 
ever, many  elements  have  more  than  one  valency,  there- 
fore they  have  more  than  one  chemical  equivalent 
weight,  as  can  be  seen  from  the  following  table : — 


Element. 

Atomic 
Weight. 

Valency. 

Chemical  Equivalent 
Weight,  ^I\ 

Hydrogen  . 

I 

I 

I 

Oxygen 

16 

2 

8 

Gold 

197 

3  or  I 

65-6    or  197 

Tin    . 

118 

4  ,,   2 

29'5     »      59 

Phosphorus 

3i 

5  i,  3 

6-02  „      10-03 

Tungsten    . 

184 

6  ,,  4 

30-6     „    .  46-0 

From  Faraday's  laws  it  can  be  seen  that,  if  the 
weight  of  any  substance  liberated  by  a  definite  current 
in  a  definite  time  is  known,  the  theoretical  weight  of  any 
substance  which  should  be  liberated  by  a  definite  current 
in  a  definite  time  can  be  calculated,  if  the  chemical  equiva- 
lent weight  of  this  substance  is  known.  Very  careful 
experiments  have  been  made  with  regard  to  the  amount 


PHYSICAL  METHODS  129 

of  silver  deposited  by  a  current  of  one  ampere  flowing 
for  one   second   (one   coulomb)  ;   this  current   deposits 

'ooi  1.  1  8  gram  of  silver 

from  an  aqueous  solution  of  a  silver  salt. 
Now  the  atomic  weight  of  silver  is 

107-94 

and  its  valency  is  unity,  therefore  its  chemical  equiva- 
lent weight  is 


but  the  atomic  weight  of  hydrogen  is 

ro 

and  its  valency  is  unity,  therefore  its  chemical  equivalent 
weight  is 

ro, 

therefore   it   follows   from    Faraday's  second   law   that 

"OOI  Il8  f    1        i  -11     i         iM 

-  ;  —  =  '000010357  gram  of  hydrogen  will  be  liber- 

ated by  one  ampere  flowing  for  one  second,  or  the  mass 
of  hydrogen  liberated  by  any  current  in  any  time  may  be 
expressed  as 

i  '0357  x   io"5A/ 

where  A  is  the  current  in  amperes  and  t  the  time  it  flows 
in  seconds  ;  which  is  equivalent  to  saying  that,  at  o°  C. 
and  760  mm.  barometric  pressure  (29-92  inches),  one 
ampere-hour  will  liberate 

'o  1  47  cubic  foot  of  hydrogen. 

So  far  the  relationship  between  current  and  volume 
of  hydrogen  which  would  be  produced  theoretically  has 
been  considered  ;  it  now  remains  to  determine  the 
relationship  between  power  and  the  volume  of  hydrogen 

9 


130     MANUFACTURE  OF  HYDROGEN 

which  should  be  theoretically  liberated.  To  refer  to 
the  diagram,  it  will  be  at  once  appreciated  that,  to  get 
the  current  to  flow  through  the  electrolyte  requires  an 
electrical  pressure,  or,  in  other  words,  there  will  be 
found  to  be  a  voltage  drop  between  the  anode  and 
cathode. 

This  voltage  drop  is  due  to  two  types  of  resistance, 
one  of  which  is  identical  to  the  resistance  of  any  con- 
ductor and  is  dependent  on  the  cross-sectional  area  of 
the  path  of  flow  of  the  current  and  on  the  length  of  the 
path,  i.e.  the  distance  between  the  plates.  The  other 
resistance  is  one  that  is  due  to  a  condition  analogous  to 
the  back  E.M.F.  of  an  electric  motor.  Assume  that 
electrolysis  has  been  taking  place  in  the  diagrammatic 
cell  and  that  the  battery  has  been  removed  ;  if  a  volta- 
meter is  then  placed  between  the  anode  and  cathode  it 
will  be  found  that  there  is  a  difference  of  potential 
between  the  two  plates  and  that  the  direction  of  this 
electromotive  force  is  the  reverse  of  that  of  the  current 
which  was  supplied  in  the  first  instance  by  the  battery. 
This  resistance  is  called  the  back  E.M.F.  of  the  cell, 
or  the  polarisation  resistance.  While  the  first  type  of 
resistance  can  be  practically  eliminated  by  placing 
the  plates  close  together,  the  second  is  not  a  function 
of  the  cell  design,  but  a  constant  of  the  electrolyte  in 
the  cell ;  therefore,  to  obtain  electrolysis  in  a  cell  it 
is  necessary  that  the  current  must  have  a  certain 
theoretical  potential  to  overcome  the  polorisation  resist- 
ance of  the  electrolyte. 

The  minimum  voltage  to  produce  continuous  elec- 
trolysis in  a  cell  whose  resistance  other  than  that  due 
to  polarisation  is  negligible  is  given  below  for  various 
aqueous  solutions  of  bases,  acids  and  salts  containing 


PHYSICAL  METHODS  131 

their  chemical  equivalent  weight  in  grams  per  litre  ;  with 
considerable  variation  in  the  degree  of  concentration  of 
the  solution  it  has  been  found  that  those  solutions  given 
below  whose  minimum  voltage  is  about  1*7  require  no 
appreciable  variation  in  pressure  to  produce  continuous 
electrolysis  :— 

Solution  of  Minimum  Voltage  for 

Continuous  Electrolysis. 

Zinc  sulphate       ......     2*35  volts1 

Cadmium  sulphate        .         .         .         ,         .     2-03  „  l 

nitrate  .         .         .         .1-98  nl 

Zinc  bromide       *         ;         .         •         .         .     1*80  ,,  1 

Cadmium  chloride        .....     1*78  „  l 

Orthophosphoric  acid 1-70  „  x 

Nitric  acid .         .      '  .         .         .         .         .      1-69  ,,  1 

Caustic  soda        .         .         .         .         .  i  -69  ,, 

„      potash     .  .  .     1-67  „ 

Lead  nitrate         .        ^         .         .         .  1-52  „  1 

Hydrochloric  acid        .         .       -.         .         .1*31  „  l 

Silver  nitrate        .......       -70  ,,  1 

Now  it  has  been  previously  deduced  from  Faraday's 
laws  that  a  current  of  one  ampere  for  one  hour  should 
produce  '0147  cubic  foot  of  hydrogen  (at  o°  C.  and  760 
mm.  pressure),  but  if  a  solution  of  caustic  soda  was  used 
the  current  would  have  had  to  be  supplied  at  i  "69  volts, 
therefore  i  x  1-69  watt-hour  produces  '0147  cubic  foot 
of  hydrogen,  or 

1000  watt-hours  produce  OI47  *  =8-7  cubic  feet. 

1-69 

But,  at  the  same  time  as  the  hydrogen  is  liberated  at 
the  cathode,  oxygen  is  being  liberated  at  the  anode,  and 
since  from  Faraday's  laws  the  volume  of  oxygen  is  one 
half  of  that  of  the  hydrogen,  on  the  electrolysis  of  a 

1  Determined  by  Le  Blanc. 


132     MANUFACTURE  OF  HYDROGEN 

solution  of  caustic  soda  i  kilowatt-hour  (B.T.  U)  theoret- 
ically produces 

8-7  cubic  feet  of  hydrogen  at  o°  C.  760  mm.  (29-92"). 
and       4-4      „  „      oxygen  „ 

The  theory  of  electrolysis  having  been  considered,  it 
remains  to  describe  some  of  the  more  important  applica- 
tions of  this  phenomenon  for  the  production  of  hydrogen 
and  oxygen. 

To  refer  again  to  the  diagrammatic  cell,  if  the 
distance  between  the  anode  and  cathode  is  great  the 
resistance  of  the  cell  is  high,  and  consequently  the  pro- 
duction of  hydrogen  is  much  below  the  theoretical,  but 
if,  on  the  other  hand,  the  distance  between  the  two 
plates  is  small,  the  gases  liberated  are  each  contaminated 
with  the  other,  hence  the  design  of  a  cell  for  the  com- 
mercial production  of  oxygen  and  hydrogen  has  of 
necessity  to  be  a  compromise  between  these  extremes. 

A  large  number  of  commercial  cells  put  the  anode 
and  cathode  comparatively  close  together,  but,  in  order 
to  obtain  reasonably  high  purity  in  the  gaseous  products, 
a  porous  partition  is  placed  between  the  electrodes  :  this, 
like  increasing  the  distance  between  the  plates,  creates 
a  certain  amount  of  resistance,  but  it  has  one  advantage 
of  the  latter  procedure  in  that  it  makes  for  compactness, 
which  is  very  desirable  in  any  plant  and  particularly  so 
in  the  case  of  electrolytic  ones,  as  one  of  the  greatest 
objections  to  their  use  is  the  floor  space  which  they 
occupy. 

A  glance  at  the  list  of  patents  at  the  end  of  the 
chapter  will  show  what  an  amount  of  ingenuity  has 
been  expended  in  the  design  of  electrolytic  plant  for  the 
production  of  oxygen  and  hydrogen.  On  account  of 
this  multiplicity  of  different  cells  it  is  intended  merely 


PHYSICAL  METHODS 


133 


to   describe    the    following,    which    are    representative 
types  :- 

j.  Filter  press  type. 

2.  Tank  type. 

3.  Non-porous  non-conducting  partition  type. 

4.  Metal  partition  type. 

Section  on  Line  A.  B. 


R  hh     •-"" 

Aj 

f 

^                  c 

"^ 

B 

Asbestos^ 

^ 

^ 

J                  \ 

s 

O 

Rubber-^ 

Porous  Partition 

Electrode 

D 

Section      Section 
onC.D.         onE.E. 
Hydrogen  Liberated 


IBr  Oxygen  Outlet 
Hydrogen  Outlet 


11 

Oxygen  Liberated 
FIG.  15. 

Filter  Press  Type. —  If,  in  the  diagrammatic  cell 
(Fig.  15),  a  plate  of  conducting  material  was  placed 
between  the  anode  and  cathode  and  the  current  switched 
on,  hydrogen  would  be  liberated  at  the  original  cathode 
and  oxygen  at  the  original  anode,  but,  besides  this,  it 


134 


MANUFACTURE  OF  HYDROGEN 


would  be  found  that  on  the  side  of  the  plate  facing  the 
original  cathode  oxygen  would  be  liberated,  while  on  its 


other  side  hydrogen  would  be  given  off  ;  thus  it  is  seen 
that  the  intermediate  plate  becomes  on  one  face  an  anode 


PHYSICAL  METHODS  135 

and  on  the  other  a  cathode.  Further,  it  will  be  found  that 
the  polarisation  or  back  E.M.F.  resistance  of  the  cell 
from  the  original  anode  to  the  original  cathode  is  doubled  ; 
thus  the  placing  of  a  conductor,  to  which  no  electrical 
connections  have  been  made,  turns  the  original  cell  into 
two  cells.  The  filter  press  cell  is  constructed  on  lines 
analogous  to  the  above. 

The  filter  press  cell  is  composed  of  a  series  of  iron 
plates,  which  are  recessed  on  either  side  as  shown  in  the 
diagram,  from  which  it  will  be  seen  that,  if  two  of  these 
plates  are  put  together,  a  space  will  be  enclosed  by  them 
by  virtue  of  the  recess. 

In  each  plate  there  are  three  holes,  one  at  X  and 
two  along  the  line  AB,  so  that,  when  the  plates  are 
placed  together,  the  enclosed  recess  could  be  filled  with 
water  by  means  of  the  hole  X.  A  small  hole  com- 
municates with  recess  and  the  holes  on  AB,  but  in  the 
case  of  one  this  communication  is  on  the  right-hand  side 
while  on  the  other  it  is  on  the  left.  Now,  between  any 
two  plates  is  placed  a  partition,  the  shape  and  holes  in 
which  exactly  coincide  with  those  in  the  plates.  The 
edge  of  this  partition  is  composed  of  rubber,  while  the 
centre  portion,  which  is  of  the  same  size  as  the  recess  in 
the  plate,  is  made  of  asbestos  cloth . 

If  four  of  these  plates  are  pressed  together  with  the 
partitions  between,  they  will  make  three  symmetrical 
cells  which  can  be  filled  with  electrolyte  by  blocking  up 
the  hole  X  in  one  outside  plate  and  running  it  in  through 
this  hole  in  the  other  outside  plate.  Since  the  asbestos 
portion  of  the  partition  is  porous,  the  electrolyte  will 
soon  reach  the  same  level  in  each  cell. 

Now,  if  a  positive  electric  connection  is  made  to  one 
outside  plate  and  a  negative  to  the  other,  what  current 


136     MANUFACTURE  OF  HYDROGEN 

passes  must  flow  through  the  electrolyte  and  consequently 
electrolysis  will  take  place.  Since  each  plate  is  insulated 
from  the  other  by  the  rubber  edge  of  the  partition  each 
plate  becomes  on  one  face  an  anode  and  on  the  other  a 
cathode,  as  was  described  in  the  diagrammatic  cell,  but 
the  two  plates  which  go  to  make  the  recess  are  divided 
by  the  asbestos  partition,  so  the  gases  liberated  have 
little  opportunity  of  mixing.  Since,  as  has  been  already 
mentioned,  one  of  the  holes  in  the  top  of  the  plate  is  in 
communication  with  one  side  of  the  recess  and  the  other 
hole  with  the  opposite  side,  the  hydrogen  and  oxygen 
formed  pass  via  separate  passages  to  different  gas- 
holders. 

The  description  is  applicable  to  all  filter  press  type 
cells.  The  actual  voltage  of  the  electrical  supply  deter- 
mines the  number  of  plates  which  are  in  the  complete 
unit,  for  the  individual  resistances  are  in  series.  In 
practice,  using  a  10  per  cent,  solution  of  caustic  potash 
as  the  electrolyte,  the  voltage  drop  per  plate  is  2 '3-2 '5. 
The  current  density  is  generally  about  18-25  amperes 
per  square  foot,  while  the  production  is  5*9  cubic  feet 
of  hydrogen  and  3  cubic  feet  of  oxygen,  at  mean  tem- 
perature and  pressure,  per  kilowatt-hour,  the  purity  of 
the  hydrogen  being  about  99^0  per  cent,  and  that  of  the 
oxygen  97*5  per  cent.1 

The  filter  press  type  of  cell  has  a  considerable  ad- 
vantage by  being  compact,  but,  on  the  other  hand,  since 

1  The  reason  for  the  difference  in  purity  is  due  to  the  fact  that  a 
small  amount  of  diffusion  takes  place  through  the  porous  partitions, 
and  since  on  account  of  its  density  the  volume  of  hydrogen  diffusing 
into  the  oxygen  will  be  greater  than  the  amount  of  oxygen  diffusing 
into  the  hydrogen,  the  purity  of  the  oxygen  must  of  necessity  be  less 
than  that  of  the  hydrogen. 


PHYSICAL  METHODS 


137 


the  water  and  gas  tightness  of  the  individual  cells  de- 
pends on  the  rubber  in  the  partition  and  on  the  method 
of  pressing  the  plates  together,  both  these  require  a 
certain  amount  of  attention  ;  probably  a  cell  of  this  type 
would  require  overhauling  in  these  particulars  about  once 
in  every  two  and  a  half  months,  if  it  were  kept  running 
continuously. 


H 


o    o 


Similar  Holes  drilled 
all  over  CylinderC. 


M 


FIG.   17.— Tank  Cell. 

The  following  are  probably  the  best-known  com- 
mercial cells  of  this  type  :  Oerlikon  and  Shriver. 

The  Tank  Cell. — This  type  of  cell  will  be  readily 
understood  by  looking  at  the  diagram  (Fig.  17).  It 
consists  of  a  circular  tank  H  made  of  dead  mild  steel, 


138 


MANUFACTURE  OF  HYDROGEN 


standing  on  insulators  M,  with  an  annular  ring  at  the 
top.  In  this  tank  an  iron  cylinder  C,  perforated  with 
holes,  is  hung  from  the  cast-iron  lid  of  the  cell  K  by 
means  of  an  electrode  E.  Between  the  side  of  the  tank 


FIG.  1 8. — International  Oxygen  Company's  Cell. 

H  and  the  cylinder  C  an  asbestos  curtain  A  is  hung 
from  a  plate  of  non-conducting  material  B.  The  lid  of 
the  tank,  which  is  insulated  from  both  H  and  C,  has  two 
flanges  O  and  N  which  form  an  annular  ring.  It  also  has 
two  outlet  pipes  G  and  F. 


PHYSICAL  METHODS  139 

The  annular  space  in  the  tank  H  is  filled  with  water, 
while  the  interior  of  the  tank  is  filled  with  a  10  per  cent, 
solution  of  caustic  soda  in  distilled  water. 

The  method  of  operation  of  the  cell  is  as  follows  :  If 
the  negative  lead  of  the  circuit  is  connected  to  D,  which 
is  metallically  fastened  to  the  tank  body  H,  and  the 
positive  lead  is  connected  to  E,  electrolysis  will  take  place 
and  hydrogen  will  be  liberated  on  the  side  of  the  tank 
H,  rising  through  the  electrolyte  into  the  annular  space 
enclosed  by  the  flanges  N  and  O  on  the  lid  K,  from 
whence  it  is  free  to  circulate  to  the  outlet  pipe  G.  While 
hydrogen  is  being  liberated  on  the  sides  of  the  tank  H, 
oxygen  will  be  liberated  on  both  sides  of  the  cylinder  C, 
from  whence  it  will  rise  up,  ultimately  finding  its  way 
through  holes  in  the  plate  B  into  the  annular  space 
enclosed  by  the  flange  N,  and  thus  on  to  the  outlet 
pipe  F. 

There  is  a  trapped  inlet  pipe  (not  shown)  in  the  cover 
K  for  introducing  further  distilled  water  from  time  to 
time,  to  replace  that  decomposed  by  the  operation  of  the 
process. 

The  voltage  drop  between  anode  and  cathode  is 
about  2*5  volts. 

The  outlet  pipes  G  and  F  are  usually  trapped  in  a 
glass-sided  vessel,  which  enables  the  working  of  the  cell 
to  be  examined. 

Fig.  1 8  shows  a  tank  cell  of  the  International 
Oxygen  Company,  which  is  not  unlike  the  diagrammatic 
cell  which  has  just  been  explained.  Tests  on  four  of 
these  cells  by  the  Electrical  Testing  Laboratories  of 
New  York  give  the  following  figures  l  : — 

1  Ellis,  "The  Hydrogenation  of  Oils  "  (Constable). 


140 


MANUFACTURE  OF  HYDROGEN 


Average 
Amps. 

Average 
Volts. 

Average 
Watts. 

Max. 
Temp. 
C. 

Temp.  20°  C.  and  Bar.  29^92  Ins. 

Cubic  Ft.  per  Hr. 

Cubic  Ft.  per 
K.W.  Hr. 

Oxygen. 

Hydro- 
gen. 

Oxygen. 

Hydro- 
gen. 

3927 

2*609 

1022 

30-1° 

3'IJ4 

6-075 

3-05I 

5'95° 

fiydrogenF\  ^Oxygen 
Outlet         \  \  Outlet 


6/ass 


-l( 

m- 

/  x 

11 

1 

IM  tej 

1 

000 

!'°ei 

too 

""" 

A 

A 

000 

•  oc 

!"  i 

000 

000 

000 

C 

.0. 

_ 

joooLJ          [. 

J 

ooc 

tot 

90 

1  —  ' 

.  J 

—  ' 

Oxygen 
Outlet 


Hydrogen 
O 


Plan  View. 


FIG.   19. 

The  purity  of  the  oxygen  was  98*34  per  cent,  and 
that  of  the  hydrogen  (from  another  test)  9970  per  cent. 

The  best-known  plant  of  this  type  is  that  of  the 
International  Oxygen  Company. 

The  Non-Conducting.  Non-Porous  Partition 
Type. — This  cell,  which  is  illustrated  by  the  diagram 
(Fig.  19),  consists  of  a  metal  tube  A,  which  forms  the 


PHYSICAL  METHODS  141 

electrode  and  gas  outlet,  and  which  is  made  of  lead  where 
an  acid  electrolyte  is  used,  and  of  iron  where  an  alkaline 
one  is  employed.  This  metal  electrode  is  surrounded 
by  a  glass  or  porcelain  tube  perforated  at  the  bottom. 

There  are  four  of  these  electrodes  per  cell,  which 
are  arranged  as  indicated  in  the  diagram.  When  the 
current  is  switched  on  the  gases  are  liberated  on  the 
electrodes  within  the  glass  tube  ;  consequently  no  mixing 
of  the  liberated  gases  can  take  place. 

The  best-known  commercial  cell  of  this  type  is  the 
Schoop. 

The  Metal  Partition  Type. — In  the  preliminary 
description  of  the  filter  press  type  of  cell  it  was  stated 
that  a  conducting  partition  between  the  anode  and 
cathode  itself  became  on  one  face  an  anode  and  on  the 
other  face  a  cathode  ;  this,  however,  requires  modifica- 
tion, as  it  is  only  true  when  the  voltage  drop  between 
the  original  anode  or  cathode  and  the  metal  partition  is 
less  than  the  minimum  voltage  required  for  continuous 
electrolysis. 

In  the  metal  partition  type  of  cell  a  metal  partition 
is  placed  between  the  anode  and  cathode.  This  parti- 
tion is  insulated  from  the  poles,  is  not  so  deep  as  the 
electrodes,  and  is  perforated  on  the  lower  edge  with 
small  holes  which,  though  reducing  the  electrical  resist- 
ance, do  not  allow  of  the  gases  mixing. 

The  best-known  cell  of  this  type  is  the  Garuti, 
which,  since  the  true  electrodes  are  only  about  half  an 
inch  apart,  gives  a  more  compact  cell  than  if  a  non- 
conducting partition  were  employed. 

Since  the  voltage  drop  between  electrodes  is  slightly 
less  for  the  same  electrolyte  than  if  a  non-conducting 


142     MANUFACTURE  OF  HYDROGEN 

partition  were  employed  the  yield  is  good,  being  about 
6' i  cubic  feet  of  hydrogen  at  mean  temperature  and 
pressure  per  kilowatt-hour.  The  current  density  is  as 
high  as  25  to  28  amperes  per  square  foot,  using  a  10  per 
cent,  solution  of  caustic  soda. 

The  advantage  of  this  type  of  cell  is  its  compactness, 
due  to  the  small  distance  between  the  electrodes,  and 
its  lightness,  due  to  the  fact  that  it  is  made  throughout 
(with  the  exception  of  the  insulating  strips)  of  mild  steel 
sheet.  However,  the  small  distance  between  the  elec- 
trodes necessitates  care  being  taken  to  prevent  an  in- 
ternal short  circuit  in  the  individual  cells. 

Castner'Kellner  Cell. — Besides  those  cells  already 
described,  the  object  of  which  is  to  produce  oxygen 
and  hydrogen,  there  are  some  which,  though  not 
designed  for  the  production  of  hydrogen,  yield  it  as 
a  by-product. 

Probably  the  most  important  of  these  electrolytic 
processes  yielding  hydrogen  as  a  by-product  is  the 
Castner-Kellner.  The  primary  purpose  of  this  process 
is  to  make  caustic  soda  from  a  solution  of  brine  ;  but 
both  hydrogen  and  chlorine  are  produced  at  the  same 
time. 

The  working  of  this  process  can  be  understood  from 
the  diagram  (Fig.  20). 

The  plant  consists  of  a  box  A,  divided  into  three 
compartments  by  the  partitions  B,  which,  however,  do 
not  touch  the  bottom  of  the  box  A.  On  the  floor  of 
this  box  there  is  a  layer  of  mercury,  which  is  of  sufficient 
depth  to  make  a  fluid  seal  between  the  compartments. 
In  the  two  end  compartments  there  are  carbon  elec- 
trodes, connected  to  a  positive  electric  supply,  while  in 


PHYSICAL  METHODS 

the  middle  there  is  an  iron  electrode,  connected  to  the 
negative  supply.  One  side  of  the  box  A  is  carried  on  a 
hinge  H,  while  the  other  is  slowly  lifted  up  and  down 
by  an  eccentric  G,  which  gives  a  rocking  motion  to  the 
contents  of  the  box. 

In  the  two  end  compartments  is  placed  a  strong 
solution  of  brine,  while  the  middle  is  filled  with  water. 
On  the  current  being  switched  on  electrolysis  takes 
place,  the  current  passing  from  the  positive  carbon  elec- 
trodes through  the  brine  to  the  mercury,  and  from  the 


A 
t£ 

£                   F 

~C 
-£ 

"3     - 

hlorine  Outlet 
A 

Hydrogen  Outlet 

B 

---- 

-  — 

—  - 

—  ~ 

- 

B 

i  — 
A 

M--I 

- 

= 

E 

1 

: 

i 

^  

A 

\ 


Mercury 
FIG.  20— Castner-Kellner  Cell. 


mercury  to  the  negative  electrode  in  the  centre  compart- 


ment. 


Now,  considering  one  of  the  end  compartments,  by 
the  splitting  up  of  the  sodium  chloride,  chlorine  will  be 
liberated  at  the  positive  electrode,  and  will  ultimately 
pass  out  at  E,  to  be  used  for  making  bleaching  powder, 
or  for  some  other  purpose,  while  sodium  will  be  de- 
posited on  the  mercury,  with  which  it  will  amalgamate. 

Owing  to  the  rocking  of  the  box,  the  sodium  mercury 
amalgam  will  pass  into  the  centre  compartment,  where 


J44 


MANUFACTURE  OF  HYDROGEN 


it  is  decomposed  at  the  negative  electrode,  in  accordance 
with  the  following  equation  :— 

2Na  +  2H2O  =  2NaOH  +  H2. 

Thus,  by  the  operation  of  the  process,  chlorine  is 
produced  in  the  end  compartments,  and  caustic  soda 
and  hydrogen  in  the  centre  one. 

The  following  patents  have  been  taken  out  for  the 
production  of  hydrogen  electrolytically  :— 


German  patent 
English      ,, 


Delmard. 

Garuti. 

Baldo. 

Garuti.  U.S. 

Garuti  &  Pompili.   English 

U.S. 

Schmidt.  German 

Hazard-Flamand.  U.S. 
Garuti  &  Pompili.   English 


Vareille.  French 

U.S. 

Aigner.  German 

Cowper-Coles.        English 
Eycken  Leroy  & 

Moritz.  French 

Schuckert.  German 

Fischer,  Luening 

&  Collins.         '  U.S. 
Moritz.  ,, 

Hazard-Flamand.     ,, 
L'Oxhydrique 

Francaise.  French 


58282. 

1890. 

16588. 

1892. 

18406. 

1895. 

534259. 

1895. 

23663. 

1896. 

629070. 

1899. 

111131. 

1899. 

646281. 

1900. 

12950. 

1900. 

2820. 

1902. 

27249. 

1903. 

355652. 

1905. 

823650. 

1906. 

198626. 

1906. 

14285. 

1907. 

397319. 

1908. 

231545. 

1910. 

1004249. 

981  IO2. 

I003456- 
459957- 


I9II. 
191  I. 
191  I. 


PHYSICAL  METHODS 

Benker.  French  patent 

Knowles  Oxygen 

Co.  &  Grant.      English       ,, 
Maschinenfabrik 

Surth.  French         ,, 

Burden.  U.S. 

Ellis. 


145 
461981.      1913. 

1812.      1913. 


Levin. 


462394.  1913. 

1086804.  1914. 

1087937.  1914. 

1092903.  1914. 

1094728.  1914. 


APPENDIX. 

PHYSICAL  CONSTANTS. 

PHYSICAL  PROPERTIES  OF  HYDROGEN. 

Critical  temperature  . 

„       pressure 

Melting  point  at  atmospheric  pressure    -  259°  C.     1  T 
Boiling  point  „  „  -  252-7°  C.f 


•     -  234°  C 

.    20  atmospheres. 


DENSITY  OF  LIQUID  HYDROGEN. 

At  boiling  point    . -07 

At  melting  point  .......     -086 

VAPOUR  PRESSURE  OF  LIQUID  HYDROGEN  (Travers  &  Jacquerod,  1902). 


Temperature°C. 
Pressure  mm. 

-258-2 

IOO 

-  2567 

200 

-  2557 
300 

-  255-0 
400 

-  254-3 
500 

-2537 
600 

-  253-2 
700 

-252-9 
760 

LATENT  HEAT  OF  HYDROGEN. 

123  cal.  per  grm. 


10 


146  MANUFACTURE  OF   HYDROGEN 

DENSITY  OF  GASEOUS  HYDROGEN. 

At  o°  C.  and  760  mm. 

•08987  grm.  per  litre. 

5*607  Ib.  per  1000  cubic  feet. 

SPECIFIC  HEAT  OF  GASEOUS  HYDROGEN. 
At  constant  pressure. 

At  atmospheric  pressure  .         .     3-402^ 

30  atmospheres         .  .         .     3788/  Lussana>  l894- 

At  constant  volume. 

At  50°  C.      .  ...     2-402     (Joly,  1891). 

VELOCITY  OF  SOUND  IN  HYDROGEN. 

At  o°  C.  =  12-86  x  io4  cm.  per  sec.  (Zoch,  1866). 

SOLUBILITY  OF  HYDROGEN  IN  WATER. 

The  coefficient  of  absorption  is  that  volume  of  gas 
(reduced  to  o°  and  760  mm.)  which  unit  volume  of  a 
liquid  will  take  up  when  the  pressure  of  the  gas  at  the 
surface  of  the  liquid,  independent  of  the  vapour  pressure 
of  the  liquid,  is  760  mm. 

Temperature.  Coefficient  of 

0  C.  Absorption. 

O -02I481 

io -OI9551 

20 -OI8I91 

30 "OI6991 

40 -oi522 

50  ... 


Temperature.  Coefficient  of 

°  C.  Absorption. 

60 

70 

80 

90 

ioo  -oi662 


TRANSPIRATION  OF  GASEOUS  HYDROGEN. 

Oxygen  ] 

Hydrogen     ........ 

UVinckler  (Ber.,  1891,  99). 

2Bohrand  Beck  (Wied.'  Ann.,  1891,  44,  316). 


PHYSICAL  CONSTANTS  147 

REFRACTIVITY  OF  HYDROGEN. 


Air      .....         .         .  „  p   rp 

I  Ramsay  &  Travers. 
Hydrogen    .  .       -473) 

RELATIONSHIP  BETWEEN  PRESSURE  AND  VOLUME. 

Were  Boyle's  Law  correct  then  the  product  of  the 
pressure  multiplied  by  the  volume  would  be  a  constant  ; 
however,  Boyle's  Law  is  only  an  approximation,  all 
gases  near  to  their  critical  temperature  being  much  more 
compressible  than  the  law  indicates.  At  atmospheric 
temperature  the  common  gases,  such  as  oxygen  and 
nitrogen,  are  very  slightly  more  compressible  than  would 
be  expected  from  theory.  Hydrogen  and  helium  under 
the  same  conditions  are  less  compressible,  hence  Reg- 
nault's  description  of  hydrogen  as  "gas  plus  que 
parfait  ". 

The  behaviour  of  hydrogen  at  low  pressures  (from 
650  to  25  mm.  of  mercury)  was  investigated  by  Sir 
William  Ramsay  and  Mr.  E.  C.  C.  Baly,  who  found 
that,  at  atmospheric  temperature,  Boyle's  Law  held 
throughout  this  range  of  pressure. 

The  relationship  between  volume  and  pressure  when 
the  latter  is  great  has  been  investigated  by  Amagat  and 
Witkowski,  whose  results  are  incorporated  in  the  graph 
(Fig.  21),  which  shows  the  relationship  between  the 
theoretical  volume  of  hydrogen  which  should  be  obtained 
on  expansion  to  atmospheric  pressure  and  that  which 
is  obtained  from  a  standard  hydrogen  cylinder.  From 
this  it  is  seen  that,  on  expansion  from  2  coo  Ib.  per 
square  inch  to  atmospheric  pressure,  9*2  per  cent,  less 
volume  of  hydrogen  is  obtained  than  is  indicated  by 
theory. 


148 


MANUFACTURE  OF  HYDROGEN 


339 J  3tqr>3  ui  p3u^, 

<J100t^S«n?rOcsj2 


mS 

Ir 


\ 


\ 


\ 


SS 


\ 


AA 


*§gS£§g§S32S 


f  *1 

I  -»  i- 

°  -  ^-^ 
?  1  l| 


Ml 

.?:§  f 


\ 


X: 


- 


\^ 


THE  JOULE-THOMSON  EFFECT. 

Down  to  at  least  -  80°  C.  hydrogen  on  expansion  by 
simple  outflow  rises  in  temperature,  which  is  unlike  all 
other  gases  with  the  possible  exception  of  helium.  The 
variation  in  temperature  for  drop  in  pressure  of  unit 
atmosphere  for  air  and  hydrogen  is  given  below  :— 


PHYSICAL  CONSTANTS 


149 


1  Variation  per 

Atmospheric  Pressure. 

Air   .         ... 

(17-1 
\gr6 

-  0-255°  C. 
-  0-203 

Hydrogen 

f  6-8 
190-3 

4-  0*089 
+  0*046 

Lift   of   Hydrogen* — Lift   of   1000   cubic    feet    of 

hydrogen  =  I2'34  x  P  *  B  lb 
460  +  T 

where  P  =  Purity  of  hydrogen  by  volume  expressed  in  percentage. 
B  =  Barometric  pressure  in  inches. 

T  =  Temperature   of  air   in   degrees  Fahrenheit  on  the  dry 
thermometer. 

This  formula  is  correct  if  the  air  is  dry.  If  it  is  wet 
a  small  correction  must  be  applied,  which  is  given  in  the 
following  curve. 

The  purity  of  the  hydrogen  is  expressed  by  volume 
on  the  assumption  that  the  impurity  is  air  or  some  other 
gas  of  the  same  specific  gravity  as  air  under  the  same 
conditions  ;  if  the  impurity  is  not  air  due  allowance  must 
be  made. 

Correction  for  Humidity  of  Air. — The  attached 
curve  gives  the  correction  which  must  be  employed  in 
the  lift  formula  for  humidity  of  the  atmosphere.  The 
difference  between  the  temperature  of  the  air  on  the  wet 
and  dry  thermometers  is  found  on  the  left-hand  side  of 
the  graph  ;  the  temperature  of  the  air  as  shown  on  the 
dry  thermometer  is  found  on  the  bottom ;  find  where 
perpendiculars  from  these  two  points  intersect  and 


1  Joule  and  Lord  Kelvin. 


MANUFACTURE  OF   HYDROGEN 

estimate  the  value  of  the  correction  from  the  position  of 
the  point  of  intersection  relative  to  the  curved  lines. 
EXAMPLE. — Let  the  air  temperature  be 


Dry. 
60°  F. 


Wet. 
50°  F. 


then  difference  is   10°   F.,   and  the   intersection  of  the 
perpendiculars  is  between  the  curved  lines  '35  and  '4  at 


05  -1  -15  -2  -Z5  -3  -35  -445  -5  -55 


20  25   30  35  40  45   50  55  60   65  70  75   80 

Temperature  of  Dry  Thermometer  in  F? 
FIG.  22. — Correction  for  Humidity  in  Ib.  per  1000  Cubic  Feet. 

a  position  which  may  be  estimated  at  "36  Ib.  ;  therefore 
•36  Ib.  must  be  subtracted  from  the  lift  per  1000  cubic 
feet  of  hydrogen  as  determined  by  the  formula  when 
the  temperature  of  the  air  by  the  dry  thermometer  was 
60°  F.  and  the  difference  between  wet  and  dry  10°  F. 


INDEX. 


ABSORPTION  of  hydrogen  by  metals,  15. 
Air,  composition  of,  7. 

—  hydrogen  in,  7. 
Aluminal  process,  44. 
Ammonia,  26. 

—  absorption  by  charcoal,  29. 

—  liquefaction,  29. 

—  properties,  27. 

—  solubility,  28. 

—  uses,  27. 
Arsine,  32. 

—  production  in  Silicol  process,  32. 

BADISCHE  Catalytic  process,  101. 

patents,  106. 

plant,  105. 

preparation  of  catalyst,  103. 

Bergius  process,  63. 

patents,  66. 

Boiling  point  of  gases,  115. 

hydrogen,  145 

Bronze,  hydrogen  in,  4. 

CALCIUM  hydride,  34. 
Carbonium-Gesellschaft  process,  108. 
Centrifugal  separation  of  hydrogen,  124. 
Cerium  hydride,  34. 
Clays,  hydrogen  in,  7. 
Critical  pressure,  114. 

of  hydrogen,  145. 

->-  temperature,  114. 
of  hydrogen,  145. 

DENSITY  of  gaseous  hydrogen,  145. 

liquid  hydrogen,  145. 

Diffusion,  separation  of  hydrogen   by, 

121. 

Discovery  of  hydrogen,  2. 
Draper  effect,  22. 

ELECTROLYTIC  cells — 
Castner-Kellner  cell,  142. 
filter  press  type,  133. 
metal  partition  type,  141. 
non-conducting,  non-porous  partition 

type,  140. 
patents,  144. 
tank  cell,  137. 


Electrolysis,  126. 

Explosions  of  mixtures  of  hydrogen  and 
oxygen,  14. 

FAT  hardening,  35. 
Ferro-silicon,  50. 


HEAT  produced  by  ignition  of  hydrogen 

and  oxygen,  17. 
Hydrik  process,  44. 
Hydriodic  acid,  24. 
Hydrobromic  acid,  23. 
Hydrochloric  acid,  21. 
Hydrogen  and  arsenic,  32. 

bromine,  23. 

carbon,  20. 

chlorine,  21. 

iodine,  24. 

nitrogen,  26. 

-  oxygen,  9. 

phosphorus,  30. 

selenium,  25. 

sulphur,  24. 

tellurium,  26. 

—  physical  constants,  145. 

—  production.       See      Production     of 

hydrogen. 

Hydrogenite  process,  60. 
Hydrolith  process,  67. 

IGNITION  temperature  of  hydrogen  and 

oxygen,  10. 

Iron  Contact  process,  86. 
Fuel  consumption,  97. 
Oxidising,  90. 
Patents,  99. 
Plant— 

Multi-retort  type,  93. 

Single  retort  type,  95. 
Purging,  89. 

Purification  of  hydrogen,  90. 
Reducing,  88. 
Secondary  reactions,  91. 
Sulphuretted  hydrogen  in,  93. 


JouLE-Thomson  effect,  148. 
LATENT  heat  of  hydrogen,  145. 


(151) 


152 


MANUFACTURE  OF  HYDROGEN 


Lift  of  hydrogen,  149. 
Linde-Frank-Caro  process,  113. 

—  patents,  121. 

—  purification  of  gas,  120. 
Lithium  hydride,  33. 

MAGNESIUM  hydride,  34. 
Manufacturing  processes — 

Badische  Catalytic,  101. 

Bergius,  63. 

Carbonium-Gesellschaft,  108. 

Electrolytic,  132. 

Hydrik,  44. 

Hydrogenite,  60. 

Hydrolith,  67. 

Iron  Contact,  86. 

Linde-Frank-Caro,  113. 

Sical,  69. 

Silicol,  45. 
Meteoric  iron,  hydrogen  in,  3. 

OCCURRENCE  of  hydrogen,  2. 

Oil  and  gas  wells,  hydrogen  in  discharge 

from,  5. 

Oxygen,  explosion  of  hydrogen  and,  14. 
—  heat  produced  by  ignition  of  hydro- 
gen and,  17. 

—  ignition    temperature   of    hydrogen 

and,  10,  15. 

—  reaction  of  hydrogen  with,  9. 

PHOSPHINE,  30. 

—  action  on  metals,  31. 
Phosphoretted  hydrogen,  30. 
Physical  constants  of  hydrogen,  145. 
Polarisation  resistance,  130. 
Potassium  hydride,  33. 
Production  of  hydrogen,  39. 

—  from  acetyline,  108. 

acid  and  iron,  40. 

acid  and  zinc,  42. 

alkali  and  aluminium,  44. 

carbon,  60. 

formate,  60. 

oxalate,  61. 

silicon,  45. 

zinc,  43. 

water  and  aluminium  alloy,  71. 


Production  from  water  and  aluminium 

amalgam,  69. 
—  silicide,  68. 

metallic  hydrides,  66. 

metals,  61. 

hydrocarbon  oils,  no. 

starch,  in. 

— •  —  steam  and  barium  sulphide,  100. 
—  —  iron,  86. 

-  water  gas,  101. 

REFRACTIVITY  of  hydrogen,  147. 
Rocks,  hydrogen  in,  3. 

SELENURETTED  hydrogen,  25. 
Sical  process,  69. 
Silicol  process,  45. 

composition  of  sludge,  55. 

lime,  use  of,  53. 

mineral  grease,  use  of,  57. 

patents,  59. 

plant,  47. 

precautions  to  be  taken,  57. 

purity  of  hydrogen  produced,  45. 

strength  of  caustic,  52. 
Sodium  hydride,  33. 
Solubility  of  hydrogen  in  water,  146. 
Sound,  velocity  in  hydrogen,  146. 
Specific  heat  of  hydrogen,  146. 
Sulphuretted  hydrogen,  24. 
removal  from  water  gas,  84 

TELLURETTED  hydrogen,  26. 
Transpiration  of  hydrogen,  146. 

USES  of  hydrogen,  i. 

VOLCANOES,  hydrogen  in  gases  from,  5. 

WATER  gas  manufacture,  72. 

Dellwick  method,  75. 

English  method,  74. 

Swedish  method,  75. 

purification  of,  82. 

removal  of  sulphuretted  hydrogen 

from,  84. 


ABERDEEN:    THE  UNIVERSITY  PRESS 


